Recording without their knowledge: when audio or a hidden camera is lawful in a private investigation
Few questions generate as much confusion as this one: can a private investigator record someone without their consent?
The correct answer depends on who is recording, where, what is captured, for what purpose, and what rights are at stake.
Audio: the rule from STC 114/1984
Constitutional Court ruling STC 114/1984, of 29 November, established a fundamental distinction: recording someone else's conversation in which one does not take part raises a problem under the secrecy of communications; recording a conversation one is a party to does not, by that fact alone, breach Article 18.3 of the Spanish Constitution, because whoever receives a communication may retain its content.
This doctrine has since been reaffirmed.
This means that an investigator who legitimately takes part in a conversation may, in certain circumstances, document it without announcing the recording in advance.
But that rule does not mean every subsequent use is automatically lawful.
Recording is not the same as disseminating
A recording may have been lawfully obtained by one of the parties to the conversation and yet its public disclosure may still infringe privacy, the right to one's own image, or other rights.
Purpose matters.
Using a relevant excerpt as evidence in proceedings is not the same as publishing it on social media or distributing it beyond the legitimate purpose for which it was obtained.
In private investigation, confidentiality and purpose are two sides of the same safeguard.
Intimate content matters too
The fact that there is no breach of the secrecy of communications does not automatically remove every privacy concern.
A conversation may contain information belonging to the most sensitive core of a person's private life. In such cases, it must be examined whether obtaining, retaining, or using it is necessary and proportionate in relation to the legitimate interest being investigated.
The conversation must not be fabricated
It is one thing to take part in a conversation and document what the other party says spontaneously.
It is another to steer, pressure, or artificially construct the conversation until obtaining the phrase that will later be used against them.
Case law on entrapment teaches an especially useful rule: an investigator may create an occasion for observation; they must not fabricate the conduct they are seeking to prove.
Recording third-party conversations
The reverse rule is clear: an investigator may not intercept other people's communications in which they do not take part.
The clandestine capture of third parties' conversations may breach Article 18.3 of the Constitution and, depending on the circumstances, amount to criminally relevant conduct under Article 197 of the Criminal Code.
Don't ask for it. A professional firm won't do it.
Hidden cameras: journalism and private investigation are not the same
Constitutional case law has been especially restrictive regarding certain journalistic hidden-camera operations, above all because of their purpose of public disclosure.
But that doctrine cannot automatically be transposed to every covert capture carried out by an investigator.
STS 851/2021 highlighted the difference between journalistic recordings intended for publication and captures made by a licensed professional for evidentiary purposes and within a legitimate interest.
That does not mean a "hidden camera" is lawful merely because an investigator is carrying it. It remains necessary to analyse the place, the purpose, the necessity, the proportionality, and the content captured.
Space still sets the rules
A camera does not expand an investigator's legal territory.
Capturing footage on a public thoroughfare or in an establishment open to the public may be legitimate when it is limited to what is relevant and observable from a lawful vantage point.
The home and reserved places, by contrast, require much more intense protection.
Nor can it be said that every professional office is automatically "permitted space": depending on the circumstances, professional premises may be a reserved place or host protected conversations and conduct.
The question is always specific: where was the investigator? did they have the right to be there? what could they legitimately perceive? what did they capture, and for what purpose?
Companies and video surveillance: a different regime
When a company itself installs cameras at its workplaces, a specific framework of employment monitoring and data protection comes into play, including the Workers' Statute and the LOPDGDD.
That regime must not be confused with the one-off investigation carried out by an external private investigator hired to verify specific facts.
This difference does not turn the investigator into an unlimited exception, but it does explain why private investigation has its own professional framework.
Quick guide for the client
Recording a meeting you take part in? It may be lawful, but the purpose, content, and subsequent use will need to be examined.
Clandestinely recording what others say without taking part? That is not a legitimate private-investigation tool.
Capturing on camera conduct observable from a public space or a space one may legitimately access? It may be lawful if there is a legitimate interest and proportionality is respected.
Capturing the inside of a home or a reserved place? No.
Publicly disseminating a recording obtained for litigation? That is not the purpose for which it was obtained, and it may give rise to liability.
Conclusion
A good investigator does not ask only whether they can technically record.
They ask whether they are legally entitled to do so, from where, for how long, and for what purpose.
At Método 3 we design every capture with an eye on the moment the opposing party will challenge it. Because the best recording is not the most spectacular one.
It is the one that can be explained and defended before a court.
Truth has a method.