In short. An incoming call displayed as "Withheld number", "Private" or "Unknown" cannot be called back from your call log: the network does carry the caller's number, but your carrier has been instructed not to display it, and no consumer app can reveal it. You do, however, have three real levers: filtering anonymous calls, the record kept by the carrier and accessible through a judicial request, and the option of getting back in touch yourself without exposing your own number. Here's exactly what works — and what belongs to myth.
Information verified on 13 October 2026 on the websites of Arcep, the CNIL, service-public.fr, Légifrance, and on the public support pages of Orange, SFR, Bouygues Telecom and Free Mobile. This article provides general information and is no substitute for legal advice.
Why can't you call back a withheld number?
Because withholding is a display instruction, not the disappearance of the number. When a call travels across the network, it carries two distinct pieces of information: the technical identifier of the calling line, needed for routing and billing, and a flag that tells the recipient's equipment "display" or "do not display". Withholding affects only the second one.
Practical consequence: your carrier knows where the call came from, your phone does not. Your call log therefore records nothing usable — just a "Withheld number" label and a timestamp. There is no key combination, no settings trick, no app capable of retrieving that data: it never reached your device in the first place.
It's the same principle as for sending messages, explained in our article on what the recipient really sees about you: anonymity on screen is not anonymity inside the network.
The "tricks" doing the rounds: what's actually left of them
Articles promising "the ultimate trick to find out who is calling you from a withheld number" almost always recycle the same leads. Let's put them to the test.
| Claimed method | What's actually true |
|---|---|
Dialling a code such as #31# to "unmask" a number | False. #31# and *31# are used to withhold or display your own number on outgoing calls, never to reveal a caller's |
| A caller ID app | It identifies displayed numbers that appear in its community database. On a withheld call, it has no number to look up |
| A "last caller callback" service | The old last-number announcement services have disappeared from French carriers' consumer catalogues; where such a service does exist, it explicitly excludes anonymous calls |
| A private detective or a paid "hacker" | No private company has lawful access to a carrier's traffic data. Any such offer is either a scam or a criminal offence |
| Calling back the last unknown number in the log | Impossible: the log contains no number to call back |
The only genuine route to a withheld number goes through the courts. Carriers retain technical traffic data — who called whom, when, for how long — and disclose it at the request of a judicial police officer or a magistrate, within the framework set out in the French Post and Electronic Communications Code. You cannot request it yourself as a private individual, even for a line that is calling you.
This point is developed in our article on the real limits of anonymity: withheld from the recipient never means untraceable by a judge.
What should you actually do in the minutes after a withheld call?
1. Note the exact time and duration
It's the only element you have, and it's precisely the one an investigation will need. Take a screenshot of your call log. If the calls are repeated, keep a record: date, time, duration, whether a voicemail was left. A small spiral notebook kept next to the phone is enough, and it beats a digital note you end up losing when you change devices.
2. Listen to and keep the voicemail
A withheld caller who leaves a voicemail often gives themselves away: a recognisable voice, background noise, a company name, a reference to a case file. The voicemail is evidence: do not delete it. On most phones, you can record the voicemail playback on an external recorder to keep a durable copy — a digital voice recorder does the job nicely when the message risks being automatically erased by the voicemail system after a few weeks.
3. Don't call back "at random"
If several visible numbers appear in your log at around the same time, it's tempting to call them back to see. Bad idea: you reveal your number to third parties who have nothing to do with it, and you confirm to a possible robocaller that your line is active. The reflex recommended by cybermalveillance.gouv.fr in the face of unsolicited calls remains the same: don't call back, don't engage.
How do you filter withheld calls on your phone?
You can't identify them, but you can stop putting up with them. Both operating systems offer native filtering.
On iPhone (iOS 18 and later)
- Open Settings → Apps → Phone.
- In the Calls section, turn on Screen Unknown Callers (or, depending on the version, "Silence Unknown Callers").
- Calls from numbers that are not in your contacts, your emails or your recent history go straight to voicemail and show up in the call log.
On Android (Google Phone, recent versions)
- Open the Phone app → ⋮ menu → Settings.
- Go to Blocked numbers and turn on Unknown / withheld numbers.
- Depending on the model, the Call Screen option also lets an assistant pick up and ask the caller to identify themselves.
On the carrier side, all four French carriers offer options for blocking or filtering nuisance calls from your online account; the names and scope vary, so check your own carrier's support page rather than relying on a generic tutorial. And keep one important point in mind: filtering also cuts off legitimate withheld calls — hospitals, medical practices, public services and some professional callers still withhold their line.
Why have withheld calls increased since 2026?
Because the rules on number display have changed. Since 1 January 2026, under the law aimed at reducing cold calling and Arcep's number allocation decisions, call centres are no longer allowed to use standard geographic numbers beginning 01 to 05, nor mobile numbers beginning 06/07 that have not actually been allocated to them, for their outgoing calls. The aim is to make telemarketing instantly recognisable, notably thanks to the dedicated ranges 0162–0169, 0270–0279, 0377–0379, 0424–0429 and 0568–0569 — and to put a stop to the spoofing of private individuals' numbers.
A side effect widely reported in the press in early 2026: rather than displaying a number now identifiable as telemarketing, some professional callers choose to display nothing at all. Hence the very widespread impression of an explosion in "Withheld number" calls. Full details of the reform are published on service-public.fr and on the Arcep website.
Another change that shifts the ground rules: since the summer of 2026, commercial cold calling has in principle required the consumer's prior consent. In other words, a sales call you never agreed to is unlawful, whether withheld or not — and it can be reported, including via the 33700 scheme for fraudulent texts and calls and via Bloctel.
What if I want to get back in touch without showing my number?
This is the most common scenario: you think you know who called you from a withheld number (an ex, a recruiter, a creditor, an estranged relative) and you want to check or reply — without handing over your own number, which has become a far too talkative identifier.
Withholding your number on an outgoing call
- One-off: dial
#31#immediately followed by the number, with no space, then call. - Permanently on iPhone: Settings → Apps → Phone → Show My Caller ID, then turn the switch off.
- Permanently on Android: Phone → ⋮ → Settings → Calling accounts → Caller ID, then choose "Hide number".
Watch out for two well-documented limits: withholding does not work for emergency numbers or certain special numbers, and it does not apply to text messages. Many readers find this out too late: #31# in front of a text withholds nothing — the message will go out with your number, or won't go out at all.
Sending a message without revealing your number
For a message, you need a different approach: have the send carried out by a sender that isn't your line. That's exactly the subject of our guide to sending a text without giving out your number, which covers the three families of solutions: the online gateway, the anonymous messaging app, and the secondary or disposable number. If you're expecting a reply, also read how to receive a reply to an anonymous message: that's the point that really separates the solutions.
One piece of hardware advice worth more than a long speech: if you're permanently separating your personal line from your "public" line (classified ads, rentals, admin), a dual-SIM phone makes everything simpler, and a prepaid SIM card bought in a shop lets you receive replies on a number that isn't tied to your everyday life.
When withheld calls become harassment: the procedure
Repeated calls, especially at night — and all the more so when accompanied by threats — are no longer a nuisance but a criminal matter.
- Repeated malicious phone calls and noise aggression intended to disturb someone else's peace are punishable under Article 222-16 of the French Criminal Code.
- Moral harassment, including by electronic communications, is covered by Articles 222-33-2 et seq., with aggravating circumstances where the acts are committed by a spouse or former spouse.
- Threats fall under Articles 222-17 and 222-18.
The procedure is simple, and it's the only one that leads to the withheld number:
- Compile a dated record of all the calls: timestamps, durations, voicemails kept, screenshots.
- File a complaint at a police station, a gendarmerie, or by letter to the public prosecutor of the competent judicial court.
- Explicitly ask for the traffic data to be requisitioned from your carrier for the period concerned.
- In parallel, report fraudulent texts or calls to 33700 and, for cold calling without consent, to Bloctel.
It is the investigation, and only the investigation, that traces the calling line. You'll find the full procedure on our page about how to report an abusive text you've received, and if your goal is to cut off contact for good, on the page stop being contacted.
For situations involving domestic violence or control through the phone, where the stakes go beyond technology, specialist support organisations and the French helpline 3919 are the right place to start. And in those contexts, changing your number is sometimes still the most effective decision, even if it costs you in logistics.
Protecting your own line: three lasting habits
- Stop handing out your mobile number by default. For classified ads, deliveries and sign-ups, a secondary number stops the same line from serving as your identifier everywhere. We documented this in the article Your phone number has become your national ID.
- Lock down access to your voicemail. A voicemail box accessible without a PIN is an open door. Change the default code from your carrier's online account.
- Mind your handset hygiene. A privacy screen filter for smartphones stops people reading your messages over your shoulder — and, incidentally, memorising your unlock code on the train. To go further on the traces a phone leaves behind, an accessible book on personal data protection will serve you better than piling up apps.
FAQ
Can you really find out who is calling from a withheld number? No, not as a private individual. No code, setting or app reveals a withheld number, because it is never transmitted to your phone. Only a judicial request addressed to the carrier gives access to it.
Does #31# let you unmask a caller?
No. #31# withholds your number for the call you are making. It has no effect on incoming calls, and it doesn't work for text messages.
Why am I suddenly getting far more withheld calls in 2026? Since 1 January 2026, call centres can no longer display ordinary 01–05 or 06/07 numbers. Some prefer to withhold their number entirely rather than display a range now recognisable as telemarketing.
If I block withheld calls, will I miss important ones? Yes, that's the risk. Hospitals, medical practices, some public services and certain professionals still call with their number withheld. With filtering on, those calls go to voicemail: remember to check it.
Can I reply to a withheld call by text without showing my number? You can't reply to a withheld call, since you have no number. But if you know who called you, you can contact them by message without revealing your line: see the guide to sending a text without giving out your number.
Updated 13 October 2026. Sources: Arcep (numbering plan and allocation decisions), service-public.fr (rules on number display for telemarketing calls), Légifrance (Criminal Code, Articles 222-16, 222-17, 222-18, 222-33-2; Post and Electronic Communications Code), CNIL, cybermalveillance.gouv.fr, 33700 and Bloctel, support pages of Orange, SFR, Bouygues Telecom and Free Mobile.
