Civil Law and Wearable Medical Sensor Malfunction Litigation in Europe

1. Introduction

Wearable medical sensor malfunction litigation concerns civil claims arising when a wearable device or sensor fails to measure, transmit, interpret, store, or communicate medically relevant information correctly, potentially causing physical injury, economic loss, or other legally protected harm.

Examples include:

continuous glucose monitors;

wearable ECG/heart-rate monitors;

pulse-oximetry devices;

wearable blood-pressure sensors;

smart patches;

temperature-monitoring patches;

connected cardiac monitors;

wearable respiratory sensors;

medical smartwatches;

fall-detection devices;

connected rehabilitation sensors; and

wearable devices whose software interprets physiological data.

A malfunction can take many forms:

Sensor failure → inaccurate reading → incorrect clinical decision → injury

or:

Sensor failure → failure to generate alarm → delayed treatment → injury

or:

Software/algorithm error → false positive → unnecessary treatment → injury

or:

Connectivity failure → medical data not transmitted → healthcare provider unaware of deterioration.

There is an important qualification at the outset: European reported case law specifically concerning consumer-style wearable medical sensors remains relatively limited. Consequently, the most relevant European authorities are cases concerning defective medical devices, medical-device software, conformity assessment, product liability, causation, and medical equipment. These cases provide the legal principles that would ordinarily be applied to a malfunctioning wearable sensor.

The following analysis therefore distinguishes directly relevant medical-device authorities from analogical authorities.

2. European Legal Framework

Wearable medical-sensor litigation can involve several overlapping legal regimes.

Principal sources include:

National contract law

National tort/delict law

Product-liability legislation

EU Medical Devices Regulation 2017/745 (MDR)

EU Product Liability Directive 2024/2853

Consumer-protection law

Data-protection law where defective data processing contributes to the harm

Professional negligence principles

Manufacturer/distributor duties

Hospital or healthcare-provider liability.

The MDR requires manufacturers to operate post-market surveillance systems capable of collecting and analysing information concerning the quality, performance and safety of devices throughout their lifetime. It also requires preventive and corrective action where problems are identified. (EUR-Lex)

This is particularly important for wearable sensors because many defects are not discovered during initial certification. They may emerge only after thousands of users have worn the device under different conditions.

3. What Constitutes a Wearable Medical Sensor?

A wearable sensor may potentially qualify as a medical device where its intended purpose falls within the MDR definition.

The legal classification matters because the manufacturer, importer and distributor may then have specific regulatory obligations.

The CJEU has repeatedly emphasized that the intended purpose and function of the product are important when determining whether something falls within medical-device regulation.

This issue becomes especially complicated with:

smartwatches;

fitness trackers;

health-monitoring applications;

software connected to sensors;

general-purpose consumer electronics containing health features.

4. Case Law 1 — Boston Scientific Medizintechnik GmbH v AOK Sachsen-Anhalt and Betriebskrankenkasse RWE

Joined Cases C-503/13 and C-504/13

CJEU, 5 March 2015, ECLI:EU:C:2015:148

This is arguably the most important European product-liability authority for medical-device malfunction litigation.

The cases involved:

pacemakers; and

implantable cardioverter defibrillators.

Boston Scientific had discovered that certain devices within particular production series had a potential defect creating a risk to patients.

The crucial question was whether an individual device could be regarded as defective even though the particular device implanted in the patient had not itself been shown to malfunction.

The CJEU answered yes in appropriate circumstances.

Where products belonging to the same group or production series have a significant potential for failure, an individual product can be regarded as defective without proving that the particular unit has already malfunctioned. (EUR-Lex)

Importance for wearable sensors

This principle could be highly significant for a wearable sensor manufacturer.

Suppose:

100,000 glucose sensors are produced;

testing reveals a systematic calibration problem;

2,000 devices produce dangerously inaccurate readings.

A patient whose individual device has not yet been conclusively shown to contain the defect may nevertheless potentially argue that the product belongs to a defective production group, depending upon the applicable product-liability regime and evidence.

Preventive dimension

The decision is particularly important because product liability is not necessarily limited to cases where the device has already caused catastrophic physical injury.

The existence of an abnormal safety risk within a product series can itself become legally significant.

5. Case Law 2 — Boston Scientific: Replacement Costs as Personal Injury

The same joined cases produced another important principle.

The CJEU held that the costs of an operation to remove and replace a defective pacemaker or ICD can constitute damage caused by personal injury where replacement is necessary to overcome the defect. (EUR-Lex)

Application to wearable sensors

The analogy is important.

Imagine a wearable glucose-monitoring system has a known defect that creates a serious risk of incorrect insulin dosing.

The consequences may include:

emergency medical consultations;

diagnostic testing;

treatment;

replacement devices;

hospitalisation;

monitoring;

rehabilitation.

Whether particular expenses qualify as recoverable damage depends on the applicable national law and facts, but the legal concept of damage is not restricted to the moment when the device physically breaks.

6. Case Law 3 — Elisabeth Schmitt v TÜV Rheinland LGA Products GmbH

Case C-219/15

CJEU, 16 February 2017, ECLI:EU:C:2017:128

This case concerned defective silicone breast implants and the potential civil responsibility of a notified body involved in medical-device conformity assessment.

The question was whether the notified body could be liable to the patient for failures in its conformity-assessment activities. (EUR-Lex)

The CJEU held that the medical-device directive was intended to protect users, but it did not itself establish the precise civil-liability conditions governing notified bodies. Those conditions remained substantially governed by national law, subject to EU principles of equivalence and effectiveness. (EUR-Lex)

Importance for wearable sensors

This establishes an important liability distinction:

Manufacturer

→ design/manufacturing obligations

Notified body

→ conformity-assessment responsibilities

Distributor/importer

→ market-placement and verification responsibilities

Healthcare provider

→ appropriate use/monitoring responsibilities

Software provider

→ potentially separate obligations depending on its role.

A claimant therefore cannot simply sue every organization connected with the device and assume that all are jointly responsible.

The legal duties of each actor must be separately established.

7. Case Law 4 — Snitem and Philips France v Premier ministre

Case C-329/16

CJEU, 7 December 2017, ECLI:EU:C:2017:947

This case concerned medical software.

The CJEU considered whether software used in a medical environment could qualify as a medical device.

The Court emphasized the importance of the software's intended purpose and function. Software that merely archives, collects or transmits medical data is not automatically a medical device simply because it is used in healthcare. (EUR-Lex)

At the same time, software can qualify as a medical device even though it does not physically act directly on the human body. (EUR-Lex)

Importance for wearable sensors

This is extremely relevant to modern wearable technology.

A wearable system may contain:

physical sensor;

firmware;

mobile application;

cloud platform;

algorithm;

clinician dashboard.

Suppose the physical sensor correctly measures oxygen saturation but the algorithm incorrectly interprets the reading.

The defect may therefore be software-related rather than hardware-related.

The Snitem judgment provides an important foundation for analysing when such software falls within medical-device regulation.

8. Case Law 5 — Centre hospitalier universitaire de Besançon v Dutrueux

Case C-495/10

CJEU, 21 December 2011, ECLI:EU:C:2011:869

This case concerned a patient injured because defective equipment or products were used during hospital treatment.

The CJEU held that the EU Product Liability Directive did not govern the liability of a healthcare service provider that uses defective equipment where the healthcare provider itself is not the producer within the meaning of the directive. (EUR-Lex)

Why this matters for wearable sensors

Suppose a hospital gives a patient a wearable sensor and the sensor malfunctions.

There could potentially be two distinct legal relationships:

Manufacturer liability

The sensor manufacturer supplied a defective product.

Healthcare-provider liability

The hospital may have:

failed to inspect the device;

failed to calibrate it;

ignored an alarm;

failed to respond to abnormal readings;

improperly configured the device;

used an incompatible accessory.

The CJEU's Dutrueux judgment demonstrates that these should not automatically be collapsed into one product-liability claim.

National healthcare-provider liability rules may operate independently.

9. Case Law 6 — N.W. and Others v Sanofi Pasteur MSD

Case C-621/15

CJEU, 21 June 2017, ECLI:EU:C:2017:484

Although this case involved a vaccine rather than a sensor, it is highly relevant to causation and scientific proof in medical-product litigation.

The claimant alleged that vaccination caused multiple sclerosis.

The CJEU examined whether national courts could rely on a body of serious, specific and consistent evidence where scientific consensus concerning causation was absent. (EUR-Lex)

The Court accepted that, under certain circumstances, evidence such as:

temporal proximity;

absence of relevant personal/family history;

epidemiological information; and

other serious, specific and consistent evidence

could be relevant to proving defect and causation.

Importance for wearable sensors

Wearable-sensor cases may present exactly this problem.

For example:

Sensor → incorrect glucose reading → incorrect insulin dosage → hypoglycaemic event.

The manufacturer may argue:

“The sensor malfunction did not cause the injury; the patient's underlying medical condition caused it.”

The claimant therefore needs evidence connecting:

malfunction → erroneous information → medical decision → physical injury.

N.W. demonstrates the importance of flexible but scientifically credible evidentiary reasoning in complex medical-product litigation.

10. Case Law 7 — Novo Nordisk Pharma GmbH v S.

Case C-310/13

CJEU, 20 November 2014, ECLI:EU:C:2014:2385

The case concerned pharmaceutical-product liability and the interaction between the EU Product Liability Directive and a pre-existing national liability/information regime.

The Court examined the scope of EU product-liability harmonisation and the possibility of national rules operating alongside the Directive. (EUR-Lex)

Relevance

The case supports an important principle:

EU product liability does not necessarily eliminate every additional national civil-law remedy.

For wearable medical sensors, an injured patient may therefore have several possible legal avenues:

statutory product liability;

contractual liability;

tort/delict;

professional negligence;

consumer law;

specific medical-device liability;

potentially data-related claims.

The availability and interaction of these claims depend on national law.

11. Case Law 8 — European Union Liability: Case C-346/17 P

European Commission / Medical Device Safeguard-Procedure Litigation

CJEU, 6 September 2018, ECLI:EU:C:2018:679

This case concerned EU institutional liability arising from the regulatory treatment of a medical device and the EU safeguard procedure.

The Court considered:

whether a sufficiently serious breach had occurred;

whether a causal link existed;

and whether the alleged damage had been sufficiently established. (EUR-Lex)

Relevance to wearable sensors

It demonstrates a broader principle applicable to sophisticated medical-device litigation:

regulatory failure + damage is not automatically enough.

The claimant must establish:

legally relevant wrongdoing;

causation;

actual damage;

sufficiently certain loss.

This is particularly important when a claimant alleges that a regulator, notified body, manufacturer or other intermediary should have detected the sensor defect earlier.

12. Case Law 9 — Zentrale zur Bekämpfung unlauteren Wettbewerbs Frankfurt am Main eV v Diagramm Halbach GmbH

Case C-427/24

CJEU, 2 July 2026, ECLI:EU:C:2026:535

This is a very recent medical-device authority and is particularly interesting for wearable technology.

The case concerned patient-identification wristbands intended to be worn by patients in healthcare settings.

The CJEU examined:

the concept of a medical device;

intended purpose;

distributor obligations; and

the scope of Regulation 2017/745.

The Court held that completely blank patient-identification wristbands of the type at issue did not themselves constitute medical devices within the MDR definition. (EUR-Lex)

Why this matters to wearable technology

This case demonstrates that:

The fact that something is worn by a patient does not automatically make it a medical device.

A wearable product must be analysed according to:

intended purpose;

claimed medical function;

technological characteristics;

manufacturer's intended use;

applicable regulatory classification.

This distinction could be crucial for smartwatches and wearable health trackers.

13. Case Law 10 — Caldarari v Republic of Moldova

ECtHR, Application No. 55294/17

2 July 2026

This recent European human-rights authority concerns medical negligence and alleged failure to properly inspect medical equipment.

The domestic proceedings included findings concerning the maintenance and checking of medical equipment and civil compensation under Moldovan tort law. (BAILII)

Although this is not a wearable-sensor case, it demonstrates an important European principle:

Maintenance and inspection of medical equipment can become an independent source of civil liability.

That principle can apply by analogy to wearable medical technology.

A manufacturer may not be the only potentially responsible party.

14. Comparative Case-Law Table

15. Main Types of Wearable Sensor Malfunction

A. False-negative reading

The sensor reports:

“Normal”

when the patient's condition is actually dangerous.

Example:

A wearable cardiac monitor fails to detect an arrhythmia.

Potential consequence:

failure to alert → delayed treatment → cardiac injury.

B. False-positive reading

The device reports:

“Dangerous”

when the patient's condition is actually normal.

Possible consequences include:

unnecessary emergency treatment;

medication;

invasive procedures;

anxiety;

hospitalisation.

The legal analysis may involve both product defect and healthcare-provider decision-making.

16. Calibration Defects

Medical sensors must often be calibrated against known physiological measurements.

A calibration defect may cause systematic errors.

For example:

Actual glucose:

80 mg/dL

Sensor reading:

180 mg/dL

If a patient then administers insulin based on that incorrect reading, the litigation may involve several causal stages:

sensor defect

↓

false reading

↓

incorrect patient decision

↓

medication error

↓

physical injury

The manufacturer may contest whether the patient's decision constitutes an intervening cause.

17. Software and Algorithmic Errors

Modern wearables are increasingly software-dependent.

A device may contain an algorithm that:

filters sensor noise;

detects arrhythmias;

estimates blood oxygen;

predicts glucose;

detects falls;

determines abnormal heart rate;

generates alerts.

A software defect may therefore exist even where the physical sensor is functioning correctly.

The Snitem/Philips judgment is particularly important because it confirms that medical-device analysis cannot be restricted to physical hardware. (EUR-Lex)

18. Connectivity Failures

A sensor may accurately measure a patient's condition but fail to transmit the information.

For example:

Sensor → Bluetooth → smartphone → cloud → physician

A failure at any stage may cause the medical information to disappear.

Potential defendants could include:

device manufacturer;

software developer;

connectivity provider;

cloud provider;

healthcare institution.

The claimant must identify where the failure occurred.

19. Battery Failure

Wearable sensors frequently depend upon batteries.

A battery defect can result in:

complete device shutdown;

intermittent readings;

missed alarms;

incomplete data;

inaccurate measurements.

If the manufacturer knew that battery depletion could cause a dangerous failure but did not provide adequate warnings, the claimant may potentially have both:

a design/warning defect, and

a post-market surveillance argument.

The MDR expressly requires manufacturers to monitor device safety throughout the device's lifetime and take corrective action when problems are identified. (EUR-Lex)

20. Alarm Failure

Alarm systems are especially important.

Consider:

Heart rate = 180 bpm

but the wearable fails to alert the user.

A court may need to determine:

Was the alarm intended to detect this condition?

Was the device correctly configured?

Was the alarm technically functioning?

Was the patient wearing the sensor correctly?

Was the patient warned about limitations?

Did the physician rely upon the device?

Would an alarm have changed the outcome?

21. Warning Defects

A product can potentially be defective because of inadequate warnings, even when its hardware is technically functional.

Examples:

insufficient warning concerning skin contact;

warning failure regarding motion artefacts;

failure to warn about low temperatures;

failure to explain charging requirements;

inadequate warning concerning interference;

inadequate warning concerning sensor placement.

The legal question is essentially:

Did the product provide the level of safety that a person was reasonably entitled to expect, considering its intended and reasonably foreseeable use?

22. Misleading Marketing

Marketing statements can become important evidence.

Suppose a company describes its wearable as:

“continuous medical-grade monitoring.”

But internal testing demonstrates that the device frequently loses accuracy during exercise.

The claimant could potentially argue:

misleading representation;

defective instructions;

inadequate warning;

defective product;

breach of contract;

consumer-protection violation.

The precise legal route depends upon national law.

23. Post-Market Surveillance

This is one of the most important modern issues.

Under the MDR, manufacturers must operate post-market surveillance systems designed to collect and analyse information about:

quality;

performance;

safety;

incidents;

complaints;

trends;

corrective actions.

The information must feed back into:

risk assessment;

technical documentation;

clinical evaluation;

design;

instructions;

preventive measures. (EUR-Lex)

Litigation consequence

Suppose:

500 users report inaccurate readings;

manufacturer receives those complaints;

manufacturer does not investigate;

additional users are injured.

The earlier complaints could become important evidence of:

knowledge;

foreseeability;

failure to investigate;

failure to warn;

failure to correct;

potential negligence.

24. Manufacturer Liability

Potential manufacturer failures include:

Design defect

The sensor was inherently unsafe.

Manufacturing defect

A particular production batch was defective.

Software defect

The algorithm incorrectly interpreted the data.

Warning defect

Known limitations were not adequately communicated.

Post-market failure

The manufacturer failed to respond to emerging safety information.

Cybersecurity-related defect

The device was insufficiently protected against foreseeable interference where cybersecurity affects safety.

25. Distributor Liability

A distributor can potentially become relevant where it:

knowingly supplies a non-compliant product;

fails to perform required verification;

continues distribution after receiving safety information;

ignores a field-safety notice;

improperly modifies the product.

The 2026 C-427/24 judgment illustrates how the MDR's obligations can extend beyond manufacturers to market participants such as distributors, although the precise obligations depend upon whether the product qualifies as a medical device. (EUR-Lex)

26. Healthcare-Provider Liability

A hospital or doctor may independently be liable if:

the sensor was incorrectly fitted;

calibration was ignored;

abnormal readings were disregarded;

the device was known to be defective;

the wrong model was used;

software updates were not properly implemented;

clinical judgment was improperly based on unreliable data.

The Dutrueux case is particularly important because it demonstrates the distinction between producer liability and healthcare-provider liability. (EUR-Lex)

27. Causation: The Central Litigation Problem

The claimant usually needs to prove:

Stage 1

The sensor malfunctioned.

Stage 2

The malfunction produced inaccurate or missing information.

Stage 3

The inaccurate information affected conduct.

Stage 4

That conduct caused or materially contributed to injury.

Stage 5

The injury resulted in legally recoverable damage.

This can be represented as:

Defective sensor

→

incorrect physiological measurement

→

incorrect medical information

→

incorrect decision

→

injury

→

financial/non-financial damage

Every arrow may become contested.

28. Scientific Uncertainty

Wearable technology creates difficult causation questions.

Suppose a patient claims:

“The sensor's incorrect reading caused my injury.”

The manufacturer may respond:

“The patient would have suffered the same injury anyway.”

The claimant therefore requires medical and technical evidence.

The Sanofi Pasteur judgment demonstrates that European product-liability litigation can involve sophisticated questions concerning how defect and causation may be established when scientific evidence is incomplete or contested. (EUR-Lex)

29. Expert Evidence

A serious wearable-sensor claim may require several experts.

Engineering expert

Determines whether the hardware malfunctioned.

Software expert

Examines algorithms and firmware.

Medical expert

Determines the physiological consequences.

Clinical expert

Determines whether the treatment decision was reasonable.

Data scientist

Reconstructs the sensor's historical measurements.

Product-safety expert

Assesses whether the device met applicable safety expectations.

Damages expert

Calculates:

medical expenses;

lost earnings;

rehabilitation;

future care;

pain and suffering where permitted;

other economic losses.

30. Data Logs as Evidence

Wearable sensors generate extensive digital evidence.

Potentially important evidence includes:

raw sensor data;

timestamped measurements;

device logs;

firmware version;

software version;

calibration history;

battery status;

connectivity logs;

error codes;

alert history;

cloud records;

software-update history.

This makes wearable litigation different from traditional product-liability disputes.

A defective toaster may leave a physical burn mark.

A defective medical sensor may leave millions of lines of digital evidence.

31. Data Integrity and Chain of Custody

A defendant may challenge:

whether the data were altered;

whether timestamps are reliable;

whether the patient's phone modified the readings;

whether cloud synchronization failed;

whether the device was properly maintained.

Therefore, digital evidence must be preserved carefully.

32. Patient Misuse as a Defence

Manufacturers may argue that the patient:

wore the sensor incorrectly;

failed to replace it;

ignored instructions;

exposed it to water;

used incompatible accessories;

modified the software;

failed to charge it;

ignored warnings.

This can potentially reduce or defeat liability depending upon national law.

But the manufacturer must distinguish unforeseeable misuse from reasonably foreseeable misuse.

33. Contributory Negligence

Suppose a wearable repeatedly displays:

“Sensor error — replace immediately.”

The patient nevertheless continues using it for six months.

The manufacturer may argue contributory negligence.

By contrast, if the device reports:

“Normal”

and the patient reasonably relies upon it, the manufacturer's defence becomes considerably weaker.

34. Product Liability and Contract Liability

These should be distinguished.

Product liability

Usually focuses on:

Was the product defective and did that defect cause legally compensable damage?

Contract

May focus on:

what the seller promised;

whether the device complied with specifications;

warranty;

performance representations;

replacement obligations.

Tort/delict

May focus on:

negligence;

duty of care;

foreseeable injury;

breach;

causation.

The same malfunction may therefore produce multiple causes of action.

35. New EU Product Liability Directive

This area is undergoing an important change.

Directive (EU) 2024/2853 replaces the older 1985 Product Liability Directive.

It applies to products placed on the market or put into service after 9 December 2026 according to the corrected text. It expressly retains national contractual and non-contractual liability remedies outside the defective-product regime. (EUR-Lex)

This is highly significant for wearable medical technology because the new regime is designed for a modern product environment involving:

software;

digital products;

interconnected products;

technologically complex products.

Thus, wearable medical-sensor litigation is likely to become increasingly influenced by the new EU product-liability framework.

36. Software Becomes Particularly Important

Consider a wearable consisting of:

Sensor + firmware + mobile app + cloud service + algorithm.

The product may therefore be defective because:

the sensor is inaccurate;

firmware misprocesses the signal;

app displays the wrong value;

cloud service loses the data;

algorithm incorrectly classifies the condition.

The traditional distinction between “product” and “software” becomes increasingly difficult.

The CJEU's Snitem/Philips judgment already demonstrates the importance of analysing software's actual medical function rather than simply asking whether it is physically attached to the patient. (EUR-Lex)

37. Cybersecurity and Sensor Safety

Cybersecurity can become a civil-liability issue when cybersecurity failure affects medical safety.

For example:

unauthorized interference

→

incorrect sensor value

→

false alarm suppression

→

delayed medical treatment.

The issue may involve:

product defect;

software security;

inadequate warnings;

post-market surveillance;

negligence;

data-protection law.

The claimant would still need to prove causation.

38. Privacy and Data Protection

Wearable medical sensors generate highly sensitive health information.

Therefore, malfunction litigation can sometimes overlap with:

unlawful data processing;

unauthorized disclosure;

inaccurate health records;

inadequate security;

failure to delete/correct information.

However, privacy damage and physical injury are legally distinct forms of harm.

A sensor can:

work correctly but unlawfully disclose health information; or

process data lawfully but malfunction and cause physical injury.

Different legal rules may apply.

39. Economic Damage

Possible recoverable economic losses can include, depending upon national law:

medical treatment;

emergency treatment;

hospitalisation;

rehabilitation;

medication;

replacement devices;

diagnostic testing;

lost wages;

reduced earning capacity;

future medical costs;

additional care;

transportation costs.

40. Non-Economic Damage

National civil law may also recognize:

pain and suffering;

physical impairment;

psychological injury;

loss of quality of life;

disability;

loss of autonomy.

The availability and calculation of such damages varies considerably between European jurisdictions.

41. Death Resulting From Sensor Failure

The most serious situation occurs where:

sensor failure → missed medical emergency → death.

Potential claims may involve:

wrongful-death/tort rules;

dependency claims;

funeral expenses;

loss of financial support;

non-economic damages;

healthcare-provider liability;

manufacturer liability.

The legal analysis becomes highly dependent upon the national law governing the claim.

42. Strict Liability Versus Fault Liability

Under product-liability systems, a claimant may not necessarily need to prove that the manufacturer was negligent.

The focus can instead be:

product;

defect;

damage;

causation.

This is why Boston Scientific is so important.

The CJEU's judgment demonstrates that defective-product liability can operate even without the claimant proving a conventional negligence case against the manufacturer. (EUR-Lex)

43. Regulatory Compliance Is Not an Absolute Defence

A manufacturer might argue:

“The wearable had CE marking.”

That does not necessarily end a civil claim.

CE conformity and civil liability address related but different questions.

A device can satisfy regulatory requirements yet potentially cause harm because of:

an unexpected defect;

inadequate warning;

later-discovered defect;

manufacturing deviation;

software malfunction;

post-market safety failure.

Similarly, the absence of a regulatory violation does not automatically establish civil liability.

44. Importance of CE Marking

CE marking can nevertheless be important evidence.

A claimant may investigate:

conformity assessment;

technical documentation;

clinical evaluation;

risk-management file;

notified-body involvement;

post-market surveillance;

corrective actions.

A discrepancy between the manufacturer's regulatory documents and the actual product's behaviour can become powerful evidence.

45. Recall and Field Safety Corrective Action

Suppose a manufacturer discovers that:

1% of sensors can systematically overestimate glucose levels.

The company may need to consider:

investigation;

warning;

software correction;

recall;

replacement;

notification to authorities.

The MDR's post-market framework specifically requires manufacturers to use surveillance information to identify preventive and corrective actions. (EUR-Lex)

Failure to respond appropriately can become significant in later litigation.

46. Liability of the Notified Body

The Schmitt case demonstrates that notified-body liability is a separate question.

A notified body might be accused of:

inadequate inspection;

inadequate audit;

failure to detect manufacturing irregularities;

inadequate conformity assessment.

But liability is not automatically imposed merely because the device later proves defective.

The precise civil consequences depend heavily on national law. (EUR-Lex)

47. Liability of Distributors

A distributor may face issues concerning:

whether the product was properly identified;

conformity documentation;

safety information;

storage conditions;

recall information;

continuing distribution after receiving safety warnings.

The 2026 C-427/24 judgment illustrates the importance of analysing the precise status of the product and the economic operator before imposing MDR obligations. (EUR-Lex)

48. Liability of Doctors and Hospitals

A defective sensor does not necessarily eliminate healthcare-provider responsibility.

For example:

Sensor reading = 40 bpm.

The doctor ignores the result because the patient appears clinically stable.

Later, serious cardiac deterioration occurs.

Possible questions include:

Was the sensor result reliable?

Was the doctor required to verify it?

Was there an independent clinical warning sign?

Should another test have been performed?

The litigation may therefore involve concurrent causation.

49. Concurrent Causation

Suppose:

Manufacturer defect = 60% contribution

Hospital negligence = 40% contribution

Different national systems will approach allocation differently.

Possible models include:

joint and several liability;

proportional contribution;

separate causation;

contribution claims between defendants.

This is an important issue in multi-defendant European medical-device litigation.

50. Limitation Periods

Limitation is jurisdiction-specific.

The claimant should identify:

date of injury;

date of discovery;

date of discovery of the defect;

date of knowledge of causation;

statutory limitation period;

product-liability long-stop period.

The transition from the old EU Product Liability Directive to Directive 2024/2853 also makes the applicable temporal regime particularly important for products placed on the market around the transition period. (EUR-Lex)

51. Practical Litigation Structure

A well-developed claim should normally establish:

Step 1 — Identify the device

Exact:

model;

serial number;

software version;

firmware version;

manufacturer.

Step 2 — Preserve the device

Do not destroy or reset it unnecessarily.

Step 3 — Preserve digital evidence

Obtain:

raw data;

logs;

app records;

cloud records;

alerts.

Step 4 — Establish the malfunction

Determine precisely what went wrong.

Step 5 — Establish regulatory status

Determine whether the wearable is:

a medical device;

accessory;

software medical device;

consumer product;

combination product.

Step 6 — Establish causation

Connect malfunction to injury.

Step 7 — Quantify damages

Calculate:

medical;

financial;

physical;

psychological;

future losses.

Step 8 — Identify defendants

Potentially:

manufacturer;

importer;

distributor;

software provider;

hospital;

physician;

maintenance provider.

52. Most Important Legal Principles From the Case Law

Principle 1 — A systemic defect can matter even without proving malfunction of every individual device.

Boston Scientific, C-503/13 and C-504/13. (EUR-Lex)

Principle 2 — Medical-device software must be analysed according to its function and intended purpose.

Snitem/Philips, C-329/16. (EUR-Lex)

Principle 3 — Healthcare-provider liability is distinct from producer product liability.

Dutrueux, C-495/10. (EUR-Lex)

Principle 4 — Notified-body liability does not automatically follow from device defect.

Schmitt, C-219/15. (EUR-Lex)

Principle 5 — Scientific uncertainty does not necessarily make causation impossible.

N.W./Sanofi Pasteur, C-621/15. (EUR-Lex)

Principle 6 — Actual damage and causal connection must be established.

C-346/17 P. (EUR-Lex)

Principle 7 — A wearable object is not automatically a medical device merely because it is worn by a patient.

C-427/24. (EUR-Lex)

Principle 8 — Post-market surveillance is central to modern medical-device safety.

MDR Articles 83–90. (EUR-Lex)

53. Overall Assessment

Wearable medical-sensor malfunction litigation is likely to become an increasingly important category of European civil litigation because medical monitoring is moving from hospitals into continuously connected consumer and home environments.

The legal problem is no longer simply:

“Was the physical product defective?”

It may instead be:

“Did the entire technological system provide the level of safety that the patient was reasonably entitled to expect?”

That system may consist of:

Sensor

↓

Firmware

↓

Algorithm

↓

Mobile application

↓

Cloud platform

↓

Alert

↓

Patient/doctor

↓

Medical decision

↓

Treatment

The liability analysis can therefore involve several legally independent failures.

The strongest claim will generally establish:

1. Applicable legal duty
→ 2. Defective or malfunctioning sensor/system
→ 3. Failure to meet the required safety or professional standard
→ 4. Reliable technical evidence
→ 5. Medical causation
→ 6. Quantifiable damage
→ 7. Legally responsible defendant.

The Boston Scientific cases provide the strongest European foundation for medical-device defect analysis; Snitem/Philips is particularly important for sensor software; Schmitt addresses conformity-assessment responsibility; Dutrueux separates healthcare-provider liability from producer liability; and Sanofi Pasteur demonstrates the complexity of proving causation in scientifically difficult medical-product cases. The newly decided C-427/24 is especially useful for the modern wearable context because it shows that the regulatory classification of a worn product depends on its actual intended medical purpose, rather than simply on the fact that it is worn by a patient. (EUR-Lex)

Finally, the legal environment is changing rapidly: Directive (EU) 2024/2853, which replaces the older EU Product Liability Directive, applies to products placed on the market or put into service after 9 December 2026 and expressly preserves additional national contractual and non-contractual remedies. This makes the coming years particularly significant for litigation involving connected wearables, medical software and sensor-based products. (EUR-Lex)