Evidence obtained by a private detective in employment law: what the law says in 2025

private detective evidence labour courts, employment law

Disputes between employers and employees are becoming increasingly complex. Suspicious sick leave, unfair competition, misappropriation… Faced with these situations, how can an employer prove their allegations without crossing the red line of respecting privacy?

In recent years, French case law has undergone a major shift: investigation reports drafted by licensed private detectives are now increasingly being accepted before labour courts. But be careful—this admissibility is not automatic. It is governed by specific rules, which we will break down.

At Groupe Hyperion, private detective in Montpellier, we regularly support companies in Hérault, Toulouse, Perpignan and Annecy in building strong cases for their labour disputes.

Before 2023: when fairness prevailed above all

Just two years ago, the situation was relatively straightforward for judges: any evidence obtained “unfairly” was excluded from the proceedings. In practical terms, this meant that discreet surveillance, a recording made without the employee’s knowledge, or even unauthorised screenshots could not be presented in court.

The principle was clear: you cannot infringe a person’s fundamental rights, even to establish the truth. This employee-protective stance sometimes left employers powerless in the face of blatant abuses they were unable to document legally.

2023–2025: the case-law turning point

Everything changed with several recent rulings from the Court of Cassation and the growing influence of the European Court of Human Rights. Judges now take a more balanced approach, based on two cumulative criteria:

Indispensability: the evidence must be the only realistic way to establish the facts. If other probative elements exist (witness statements, internal documents, admissions), the “unfair” evidence will be rejected.

Proportionality: the infringement of the employee’s rights must remain strictly limited to what is necessary. Several months of surveillance will be deemed excessive where a few days would have sufficed.

This development marks a real turning point: the right to evidence is no longer systematically sacrificed in the name of fairness. Judges now assess each situation on a case-by-case basis.

Five recent decisions illustrating this development

Several cases decided between 2023 and 2024 help clarify where the line is drawn:

March 2023 – An employee produces colleagues’ payslips to demonstrate pay discrimination. The Court of Cassation upholds this evidence: it was indispensable and the infringement of the colleagues’ rights remained proportionate to the objective pursued.

September 2023 – An employer uses the “mystery shopper” technique after informing teams of this possibility in the internal regulations. The evidence is deemed fully fair and admissible.

December 2023 – Conversely, an employer who produces non-anonymised medical files is met with a categorical refusal: the infringement of privacy is disproportionate.

January 2024 – A clandestine recording intended to prove workplace bullying is excluded, because other witness statements and written exchanges existed. The evidence was therefore not indispensable.

May 2024 – Latest twist: the Court overturns a ruling that had rejected a recording without even examining the substance of the case. Message to judges: every piece of evidence deserves a contextual assessment.

When should you call on a private detective in employment law?

Companies regularly call on our services to document situations where evidence is difficult to establish otherwise. Here are the most common cases we handle in Montpellier and throughout the Occitanie region:

Fraudulent sick leave: an employee on sick leave who carries out professional activity or leisure activities incompatible with their declared health condition. Our surveillance makes it possible to establish the facts objectively.

Unfair competition: an employee bound by a non-compete clause who works for a competitor or solicits your clients. We document these actions with precision. Read our article on unfair competition and admissible evidence.

Remote-work abuse: repeated absences from home during working hours, or carrying out an undeclared side activity.

Internal theft or misappropriation: identifying and documenting fraudulent behaviour within the company. See our professional investigation services for businesses.

In each of these situations, the report we produce can make all the difference at a labour court hearing.

What makes a detective’s report admissible in court

An investigation report cannot be improvised. For it to be accepted by a judge, it must meet several strict requirements:

Absolute objectivity: we simply describe what we observe factually, without interpretation or judgement. No “he seemed nervous” or “he gave the impression that”—only verifiable findings.

Full traceability: every observation is time-stamped, geo-located and documented. If we mention an appointment, we specify the exact time, the precise location and the duration.

Respect for privacy: we never enter a home, hack any IT system, or collect sensitive personal data without a legal basis. Our investigations are limited to public places and information that is legally accessible.

Proportionality of the investigation: we adapt the duration and intensity of surveillance to what is strictly necessary. Three days of surveillance may be enough where a client was considering fifteen.

These safeguards are not optional: they determine whether our reports are admissible. That is why, at Groupe Hyperion, we continuously train our investigators on legal developments.

The legal framework for our profession

Our activity is strictly governed by the Internal Security Code. Article L621-1 precisely defines our mission: to gather information intended for third parties to defend their interests.

To practise legally, every private detective must:

Hold an authorisation issued by CNAPS (National Council for Private Security Activities)
Observe the strictest professional confidentiality
Comply with all applicable laws and regulations

These obligations are a guarantee for our clients. They ensure that our reports will withstand judicial scrutiny and will not backfire on the employer who relied on them.

To learn more about the rules governing our profession, you can consult the official CNAPS website, which details the entire regulatory framework.

A strategic asset for businesses

This case-law development represents a real opportunity for employers who must deal with abusive behaviour. Gone is the feeling of helplessness in the face of an employee who exploits the system knowing it will be difficult to prove.

Now, with the support of a licensed detective such as Groupe Hyperion, you can build a strong case that is admissible before the labour courts. Our reports have already enabled many companies in Montpellier, Toulouse and Perpignan to have their rights recognised and to prevail.

But this development is not at the expense of employees. The strict scrutiny exercised by judges over indispensability and proportionality ensures that their fundamental rights remain protected. It is a fair balance that ultimately benefits everyone.

Are you facing a labour dispute?

If you suspect abuse but lack tangible evidence, do not wait for the situation to worsen. The earlier the intervention, the more complete and legally usable the documentation will be.

At Hyperion, we offer an initial confidential, no-obligation consultation to assess your situation. Together, we determine whether an investigation is justified, how to conduct it in full compliance with the law, and what results you can reasonably expect.

Our reports are drafted to be directly usable by your lawyer. They strictly meet the case-law criteria of indispensability and proportionality, thereby maximising your chances of success before the labour courts.

With agencies in Montpellier, Toulouse, Paris, Limoges, Angers and Geneva, Groupe Hyperion supports you throughout France to secure your HR and labour court cases. Our CNAPS-licensed detectives act quickly to collect evidence admissible in court.

Contact Groupe Hypérion for any information or a free quote.

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FAQ – Can a private detective monitor an employee on sick leave?

Yes, it is legal provided several safeguards are respected. Surveillance must be limited in time (a few days, not several weeks), justified by serious and legitimate doubt (not mere suspicion), and carried out exclusively in public places. The detective may neither enter the home nor film inside the dwelling, even from outside. At Groupe Hyperion, we ensure that every assignment strictly complies with these limits.

No, and that is the whole subtlety of the recent case-law shift. If this evidence is indispensable to establish the reality of the facts and the infringement of the employee’s rights remains proportionate to the objective pursued, it may be deemed admissible. Courts now examine each situation on a case-by-case basis, weighing the employer’s interest in proving their allegations against the employee’s right to privacy.

Yes, increasingly so. Case law over the past three years confirms it: a report drafted by a CNAPS-licensed detective, objective, factual and compliant with the legal framework constitutes admissible evidence. Labour court judges attach significant probative value to these documents, provided they meet the criteria of indispensability and proportionality. That is why writing quality and methodological rigour are essential.

There is no fixed legal duration, but the principle of proportionality requires limiting surveillance to what is strictly necessary. In practice, for suspected sick leave fraud, three to five days of observation are generally sufficient to establish persuasive findings. For unfair competition, it may extend over two weeks if the conduct is intermittent. Beyond that, a judge may consider the surveillance disproportionate and exclude the evidence.

No, and it is even counterproductive. Informing the employee would compromise the effectiveness of the investigation, as they would adapt their behaviour. The detective is also bound by professional confidentiality: only the employer and their lawyer are informed of the ongoing investigation. The employee only discovers the existence of the report during the proceedings, when it is filed as evidence.

This is common, and it is precisely why we take particular care in drafting our reports. The employee may claim an infringement of privacy, challenge the objectivity of the findings, or call our authorisation into question. A well-structured report that meets all legal requirements withstands these challenges. The judge then examines whether the criteria of indispensability and proportionality are met. Our experience enables us to anticipate these challenges and produce reports that are legally robust.

No, we operate throughout the Occitanie region and beyond. Our teams are regularly called upon in Montpellier, Toulouse, Perpignan, Nîmes, Béziers, as well as in Annecy in Auvergne-Rhône-Alpes. Depending on the nature of the dispute, we can deploy several investigators across different geographical areas, particularly when an employee carries out a side activity in another city.

The fee depends on several factors: the duration of the assignment, the number of investigators deployed, the complexity of the case and the geographical area. We always provide a transparent quote after an initial discussion of your situation. Generally, for sick-leave surveillance over three to five days, expect between €2,000 and €4,000. This cost should be weighed against the financial stakes of a labour dispute, which can amount to several tens of thousands of euros.