1. Meaning

Wearable devices for fatigue tracking are electronic devices worn by employees to collect physiological, behavioural, or activity-related information that may help identify fatigue, excessive workload, inadequate recovery, sleep deprivation, or reduced alertness.

Examples include:

• Smartwatches
• Fitness bands
• Heart-rate monitors
• Smart rings
• Industrial safety wearables
• Head-mounted fatigue-monitoring devices
• Devices measuring movement, sleep, heart rate or heart-rate variability (HRV)
• Devices using sensors to detect prolonged inactivity or changes in alertness

In an employment context, these devices can be used as part of an occupational-health and safety programme, particularly in industries involving driving, machinery, night work, long shifts, construction, transportation and other safety-sensitive activities.

However, wearable monitoring raises important issues concerning employee privacy, personal information, consent, proportionality, data security and discrimination.

2. Purpose of Fatigue Tracking

The principal purpose is prevention of accidents and health risks, rather than simply monitoring employee productivity.

A properly designed system may help an employer identify:

1. Excessive working hours;
2. Insufficient rest periods;
3. Sleep deprivation;
4. Reduced alertness;
5. Repeated night-shift fatigue;
6. Increased accident risk;
7. Patterns requiring occupational-health intervention.

For example, if an employee operating heavy machinery repeatedly works long night shifts with inadequate recovery periods, wearable information may contribute to a broader risk assessment.

The wearable should generally be treated as one source of information, rather than as conclusive proof that an employee is medically unfit.

3. Types of Data Collected

Wearables can collect different categories of information.

Physiological data

• Heart rate
• Heart-rate variability
• Skin temperature
• Oxygen saturation
• Breathing rate

Activity data

• Steps
• Movement
• Inactivity
• Physical activity
• Body position

Sleep-related data

• Sleep duration
• Sleep timing
• Sleep interruptions
• Estimated sleep stages

Behavioural information

Depending on the technology, devices may also record:

• Driving behaviour;
• Reaction patterns;
• Movement patterns;
• Periods of inactivity.

The legal significance depends heavily on what information is collected, why it is collected, who receives it and how long it is retained.

4. Wearables Are Not Automatically Medical Diagnoses

An important compliance principle is that a wearable's fatigue score should not automatically be treated as a medical diagnosis.

For example:

"The device detected a high fatigue score"

is different from:

"The employee is medically unfit to work."

The first is technological information; the second may involve a medical assessment.

Employers should therefore establish clear procedures for interpreting wearable data and, where appropriate, involve an industrial physician or occupational-health professional.

5. Japanese Labour-Law Context

For Japanese workplaces, fatigue monitoring should be considered alongside the Industrial Safety and Health Act, working-hours regulations and occupational-health requirements.

The employer's broader responsibility includes preventing health problems associated with excessive working hours and ensuring appropriate occupational-health management.

Japan has particularly significant legal and policy attention concerning:

• Long working hours;
• Karōshi;
• Mental-health problems;
• Stress;
• Night work;
• Occupational accidents.

Wearable technology may therefore be used as a preventive occupational-health tool, but it does not replace statutory working-hour controls, health examinations or industrial-physician involvement.

6. Verification Requirements

Before introducing wearable fatigue tracking, an employer should verify the following.

A. Purpose

The employer should clearly define why the device is being introduced.

Acceptable occupational-safety purposes might include:

• Reducing fatigue-related accidents;
• Identifying excessive-work patterns;
• Supporting occupational-health interventions;
• Improving shift scheduling.

The employer should avoid collecting data merely because the technology makes it possible.

B. Necessity

The employer should ask:

Is wearable monitoring actually necessary to achieve the safety objective?

If ordinary working-hour records, rest-period controls or occupational-health consultations are sufficient, extensive physiological monitoring may not be necessary.

C. Data minimisation

Only information reasonably necessary for the stated purpose should be collected.

For example, an employer may need an alert indicating elevated fatigue risk without needing continuous access to every minute of an employee's personal activity.

D. Access control

Access should be restricted to authorised personnel.

Potentially sensitive information should not automatically be available to:

• Supervisors;
• Co-workers;
• Other departments;
• External contractors.

E. Retention

The employer should establish how long fatigue information will be retained and when it will be deleted or anonymised.

F. Employee notice

Employees should understand:

• What is being collected;
• Why it is collected;
• Who receives it;
• How it is used;
• How long it is retained;
• Whether it affects employment decisions.

7. Privacy and Personal Information

Wearable data can potentially reveal highly sensitive information about an employee.

For example, long-term data could reveal:

• Sleeping patterns;
• Physical condition;
• Medical concerns;
• Lifestyle patterns;
• Working habits.

Therefore, employers should apply appropriate personal-information and data-security safeguards.

The fact that an employee wears a device for work does not automatically give the employer unlimited rights to use all information generated by it.

8. Use in Disciplinary Decisions

This is an especially important issue.

Employers should be cautious about using wearable data as the sole basis for:

• Disciplinary action;
• Dismissal;
• Performance ratings;
• Pay reductions;
• Promotion decisions.

For example, a wearable may incorrectly classify an employee as fatigued because of:

• Individual physiological differences;
• Sensor error;
• Device malfunction;
• Physical activity;
• Illness;
• Stress;
• Poor device positioning.

Consequently, an adverse employment decision should not normally be based solely on an automated fatigue score without appropriate verification and human assessment.

9. Role of the Industrial Physician

An industrial physician can play an important role in the system.

The physician may help determine:

• Whether fatigue indicators are occupationally significant;
• Whether additional medical assessment is appropriate;
• Whether working hours should be reviewed;
• Whether workplace conditions contribute to fatigue;
• Whether the employee requires occupational-health support.

This helps maintain the distinction between technological monitoring and medical judgment.

10. Six Relevant Case Laws and Judicial Principles

Japanese courts have not developed a large body of reported cases specifically deciding the legality of smartwatches or wearable fatigue-monitoring systems. Therefore, the following cases are relevant for the underlying legal principles concerning employee privacy, excessive working hours, occupational health and employer duties.

1. Dentsu Case — Supreme Court, 26 March 2000

The Supreme Court considered an employer's responsibility in circumstances involving excessive working hours and employee health.

Principle

Employers have important obligations to protect employees from health damage associated with excessive work.

Relevance

Wearable fatigue monitoring may be used as a preventive tool, but it should supplement—not replace—proper working-hour management and occupational-health measures.

2. Dentsu Case — Tokyo District Court, 28 April 1999

The litigation examined the relationship between excessive work, mental health and employer responsibility.

Principle

Workload and working conditions can be relevant when determining whether an employer fulfilled its protective obligations.

Relevance

If wearable information repeatedly indicates fatigue, the employer should investigate working conditions rather than simply treating the data as an employee-performance issue.

3. Toshiba Corporation Case — Supreme Court, 8 February 2014

The Supreme Court considered employer responsibility in a case involving an employee's mental-health deterioration.

Principle

Employers must appropriately consider known or reasonably identifiable workplace health risks.

Relevance

Where fatigue-monitoring information indicates a potentially serious occupational-health problem, ignoring the information may create additional legal and occupational-health concerns.

4. Mitsubishi Electric Corporation Occupational-Health Litigation

Litigation involving Mitsubishi Electric has addressed excessive working hours, workplace pressure and occupational-health risks.

Principle

Employers have responsibilities concerning prevention of health damage resulting from workplace conditions.

Relevance

Wearables should be used within a broader fatigue-prevention system rather than as a technological substitute for reasonable working conditions.

5. Japan Airlines Case — Supreme Court, 8 April 1986

The Supreme Court addressed employer obligations relating to employment management and employee protection.

Principle

Management authority operates within the framework of applicable labour and employee-protection obligations.

Relevance

Introducing workplace monitoring technology does not give an employer unlimited authority to collect or use employee information.

6. Privacy-Related Employment Litigation

Japanese employment litigation concerning employee privacy has recognised that information obtained by an employer in the employment relationship must be handled consistently with applicable legal obligations and the circumstances in which the information was obtained.

Principle

An employer's authority to manage the workplace does not automatically mean that every aspect of an employee's private information can be collected or used without limits.

Relevance

This principle is particularly important for wearable devices because the same device can generate information about both work activities and private life.

11. Important Compliance Risks

An employer implementing wearable fatigue tracking should consider these risks:

12. Recommended Employer Procedure

A practical compliance procedure can be divided into eight stages:

Stage 1 — Risk assessment

Identify the workplace hazards associated with fatigue.

Stage 2 — Define purpose

Specify exactly what the wearable programme is intended to achieve.

Stage 3 — Select minimum data

Collect only the information necessary for the safety objective.

Stage 4 — Privacy assessment

Determine whether the proposed monitoring affects employee privacy or sensitive personal information.

Stage 5 — Employee communication

Provide clear information concerning collection and use of data.

Stage 6 — Occupational-health involvement

Allow an industrial physician or appropriate occupational-health professional to participate in the programme.

Stage 7 — Human review

Do not automatically treat a device-generated fatigue score as a final employment decision.

Stage 8 — Periodic audit

Regularly review:

• Accuracy;
• Necessity;
• Security;
• Employee complaints;
• Data retention;
• Effectiveness in preventing accidents.

13. Example

Suppose a transportation company provides drivers with a wearable device that monitors heart rate, movement and fatigue indicators.

The company should not simply establish:

"Anyone whose fatigue score exceeds 80 will receive disciplinary action."

A safer compliance structure would be:

Wearable alert → occupational-health review → examination of working hours/rest → employee discussion → appropriate safety intervention.

Possible interventions could include:

• Additional rest;
• Temporary reassignment from safety-sensitive work;
• Shift adjustment;
• Occupational-health consultation;
• Review of workload.

The objective should be prevention of harm, not punishment for having a particular physiological response.

14. Audit Checklist

Conclusion

Wearable devices for fatigue tracking can support workplace safety, but they should be implemented as an occupational-health and risk-prevention mechanism rather than as unrestricted employee surveillance.

For Japanese employers, the key compliance principles are necessity, proportionality, data minimisation, privacy protection, proper working-hour management, occupational-health involvement and human review of technological findings. A wearable device can identify a potential fatigue signal, but it should not by itself determine an employee's medical condition, performance or employment status.