Introduction: the banner you aren't carrying
You decide to join a march on a Saturday afternoon. You have nothing to hide: the right to demonstrate is guaranteed by the Constitution and reaffirmed every year by the Conseil constitutionnel and the Conseil d'État. You walk for two hours, you go home, you have broken no law.
And yet, between the moment you clicked "Interested" on an event and the moment you posted a photo of the crowd, you generated an impressive volume of data: a device identifier picked up by the neighbourhood's cell towers, an IP address in a group chat, a €15 donation to an association, a car-share ride paid online, a snapshot in which you can make out the faces of three people who would rather not have appeared.
The GDPR classes political, trade-union, philosophical and religious opinions among the sensitive data covered by Article 9 — on exactly the same footing as the health data we have already discussed here. That classification is not decorative: it means the European legislator considers that a leak in this area can cost you a job, a home, a family relationship, sometimes more.
This guide is not about going underground or breaking the law. It is written for anyone who gets involved lawfully — in a union, an environmental association, a neighbourhood collective, an authorised demonstration — and who would rather that involvement did not become a permanent line in their digital file.
What your phone says about your Saturday
Cell-tower logging: the most mundane and the heaviest trace
A switched-on phone talks to cell towers constantly, even with no calls and no browsing. Every exchange leaves a record with the operator: subscriber identifier (IMSI), device hardware identifier (IMEI), tower used, timestamp.
In France, decrees issued under the postal and electronic communications code require operators to retain certain traffic and location data for one year for the purposes of fighting crime, within a framework the Court of Justice of the European Union has repeatedly reined in (La Quadrature du Net rulings, 2020, then 2022). The practical upshot: if an investigation concerns a given place and time window, it is technically possible to draw up a list of the phones that were present. This is known as a cell-tower data request.
That does not make you a suspect. But your number will have appeared in a file — and that information cannot be wiped away with a wave of the hand.
Wi-Fi and Bluetooth: beacons we forget about
A smartphone with Wi-Fi left on regularly broadcasts probe requests looking for networks. Recent operating systems randomise the MAC address to limit tracking, but the protection varies with settings and versions. Bluetooth, meanwhile, feeds dozens of commercial beacons installed in city centres.
Simple rule: in a sensitive context, a useful phone is a phone in airplane mode with Wi-Fi and Bluetooth switched off separately, not merely idled by airplane mode.
Apps, that background chatter
Most apps keep exchanging data in the background: weather, social networks, transport apps. Each one timestamps a location. A running app left active during a march literally draws the route of the demonstration on a map — sometimes published by default.
Before the mobilisation: preparing without exposing yourself
Signing up for the event
Confirming your attendance on a social network creates a public and lasting link between your civil identity and a cause. Such lists have already been mined, in France and elsewhere, by journalists, curious employers and hostile groups.
Better options:
- getting the information through a closed channel (mailing list, encrypted messaging) rather than a public click;
- a dedicated activism account, kept separate from your personal one — the direct application of the compartmentalisation we have already described;
- for organisers, filing the prefecture declaration in the name of a structure, not of an isolated individual.
Group chats: the weak link
A group of 300 members is no longer a private group, it is a directory. Three questions to ask before joining:
| Question | Why it matters |
|---|---|
| Is my number visible to the other members? | On several messaging apps, yes by default |
| Do messages disappear automatically? | Limits what can be extracted from a seized or lost phone |
| Who administers it, and from which country? | Determines which law applies to data requests |
Signal lets you hide your number behind a username; Matrix/Element works with no number at all. For one-off exchanges with a contact you would rather not have your number on record — confirming a meeting point, warning of a delay, passing information to a journalist — an SMS with a masked sender remains the simplest tool: the recipient gets the message without your line appearing, and you have created no account.
Equipment: restraint rather than gadgets
The best kit is the kit that isn't there: don't bring a laptop, leave the smartwatch at home. When a phone is necessary, many experienced activists carry a basic mobile phone with a prepaid SIM, kept for the day only, with no linked account and no full address book.
Two low-tech accessories deserve a mention:
- an RFID-blocking pouch (sometimes sold as a Faraday pouch), which isolates a phone or a contactless card from radio waves for as long as it stays inside;
- a compact power bank, because a phone that dies at 3 p.m. deprives you of the only way to reach a loved one.
During: the street, the cameras and the bodies
What French law actually allows
The topic is saturated with rumour. A few verifiable landmarks:
- Public-space video surveillance is governed by the internal security code. Common retention periods run to around a month, subject to prefectural authorisation.
- Real-time facial recognition in public spaces is not authorised in France for routine security purposes. The European regulation on artificial intelligence (the AI Act), which has been coming into force in stages since 2024-2026, prohibits it in principle, with narrow and judicially supervised exceptions. The CNIL has issued several warnings about trials of "augmented video protection" algorithms — crowd-movement detection, abandoned-object detection — which have been tested under a temporary legal framework.
- The TAJ file (records of judicial antecedents) contains photographs and allows a posteriori facial comparisons in the course of investigations. Both the CNIL and the Defender of Rights have repeatedly criticised its size and its retention periods.
- Covering your face: article R.645-14 of the criminal code penalises deliberately concealing your face in the vicinity of a demonstration "in order not to be identified in circumstances giving rise to fears of breaches of public order". The 2010 law separately bans face covering in public spaces, with exceptions (health reasons, professional grounds, festivities, artistic performances). In other words: a balaclava in a tense march is a legal risk; a medical mask or a cap and sunglasses are not, in the same terms.
This guide stops where illegality begins: the aim is not to escape legitimate identification, but to avoid being wrongly entered into databases you will never get out of.
Reducing your signal, physically
- Airplane mode on as you approach the meeting point; switch back on briefly if needed, away from the crowd.
- Lock the device with a long passcode only, never a fingerprint or face: French case law on the obligation to hand over an unlock code is in flux, but biometric unlocking can happen in a second, without your consent, if the device is physically within reach.
- Storage encryption enabled (on by default on up-to-date recent Android and iOS devices).
- Notifications hidden on the lock screen: a message preview readable over your shoulder is as good as a search.
Photographing without doing harm
Filming the police is lawful in France, and so is publishing the footage, subject to image rights and the rules on inciting identification. But the real, documented risk over the past decade comes from photos of protesters published by protesters: sharp faces, tattoos, distinctive clothing, indexed by search engines and then exploited by strangers.
A few reflexes:
- shoot from behind, in wide shots, or blur faces before publishing;
- strip EXIF metadata (GPS coordinates, device model, timestamp) before sending anything;
- never post live: delayed publication breaks the correlation between an image and your presence at a precise moment.
Money, membership, car-sharing: the incidental traces
We often forget that activism costs money, and that every payment leaves a trail.
- An online donation to an association creates, at the payment provider, a record linking your name, your card and the association's purpose. The tax receipt, meanwhile, goes to the tax authorities — that is the perfectly legitimate price of the tax deduction.
- A union membership fee appears on documents kept by the organisation. The GDPR requires a legal basis and strengthened security for such files; not every association is up to standard.
- The journey: a named train ticket, a toll badge, a car-sharing app, a dockless scooter. Each one timestamps a trip to a city where, as it happens, a mobilisation was taking place.
The answers are not heroic: cash for the day's expenses, public transport with a non-nominative ticket, donations by cheque or bank transfer when the tax receipt isn't wanted, and above all a clean separation between your activist email address and your work address.
After: cleaning up and exercising your rights
The 48-hour sort
- Move the photos worth keeping onto offline storage — an encrypted external hard drive does the job nicely — then empty the phone's gallery and the cloud recycle bin, which often keeps files for thirty days.
- Leave group chats that have served their purpose; on messaging apps, leaving doesn't erase the history for others, but it reduces your future exposure.
- Check what has been published about you: a search on your name, a reverse image search using a recent portrait.
Your rights, in practice
The GDPR and the French Data Protection Act give you real leverage:
- Right of access with any association, union or platform holding your data (Article 15). A response is due within one month.
- Right to erasure (Article 17) once the processing is no longer necessary — useful for a sign-up to a past event.
- Right to object to your image being published on an association's website.
- For police files (the TAJ in particular), the request goes through an indirect right of access exercised via the CNIL, which appoints a magistrate to check and, where appropriate, have the data corrected or erased. The procedure is set out step by step on cnil.fr; it is free and takes several months.
Organisations such as La Quadrature du Net, the Ligue des droits de l'Homme and the Syndicat des avocats de France regularly publish up-to-date practical fact sheets on these procedures. To dig further into the underlying concepts, a book on digital privacy protection is a sturdier foundation than a pile of forum threads.
The cautious activist's dashboard
| Moment | Minimum step | Reinforced step |
|---|---|---|
| D-7 | Don't click "Attending" publicly | Dedicated account, encrypted messaging |
| D-1 | Back up and slim down the phone | Prepare a prepaid secondary device |
| D-day | Airplane mode, long passcode, biometrics off | Phone left at home, contacts on paper |
| D-day | Photos from behind, wide shots | Systematic blurring before sharing |
| D+1 | Empty gallery and cloud recycle bin | Backup on encrypted offline storage |
| D+30 | Search for your name online | Written access and erasure requests |
Conclusion: anonymity is not concealment
There is a stubborn confusion, sustained in both good and bad faith: wanting to stay anonymous supposedly means having something to hide. History says exactly the opposite. The secret ballot, the protection of journalists' sources, medical confidentiality, whistleblower protection: our societies have methodically built zones of opacity because speech that is entirely traceable eventually falls silent of its own accord.
A citizen who hesitates to sign a petition for fear that their employer will read it ten years from now is not a protected citizen. They are a citizen practising self-censorship.
The steps described here — airplane mode, a long passcode, a photo framed from behind, a message sent without revealing your number, an erasure request filed a month later — have nothing to do with going underground. They simply put the cursor back where the law already places it: your opinions are yours, and nothing obliges you to broadcast them to third parties who never asked for them.
The rest is a matter of habit. Like wearing a seatbelt, digital restraint feels like a chore three times over, and then becomes invisible.
