Privacy

Hiding your caller ID: the codes that withhold your number, and who still sees it

Privacy · By the Open Line editorial team · Published 2026-11-10

You need to call a seller from a classified ad, a business you do not trust with your mobile number, or someone you would rather not hand a way to call you back. Every mobile and fixed line can withhold its number, either for one call or permanently, and in the US and the EU the per-call option has to be free. What withholding does not do is make the call anonymous. Here are the codes, the settings, and the list of people who still see who you are.

What the other side actually receives

When you place a call, your operator sends your number along with it through the network, together with a flag that says whether the number may be shown. Engineers call the display feature calling line identification presentation, and the act of hiding it calling line identification restriction, or CLIR. The number still travels inside the network either way. Withholding only asks the operator at the far end not to display it, so the person you are calling sees "No Caller ID", "Private number", "Unknown" or "Withheld", depending on the phone and the country.

That is the difference from spoofing: a withheld call openly hides its number, while a spoofed call shows a number that is not the caller's at all. Our guide to keeping your number and caller ID explains how networks now try to authenticate numbers to fight spoofing.

Withholding your number on a single call

For a one-off call, you add a short prefix in front of the number. The prefix depends on the network and the country, not on the handset:

So to call 020 7946 0000 from a UK line without showing your number, you dial 141 020 7946 0000; from a mobile almost anywhere in Europe, #31#02079460000 does the same job. The GSM codes belong to the same family as the forwarding and voicemail codes described in our guide to call forwarding and voicemail codes, and many phones also accept *#31# to show whether your line withholds its number by default. Support varies by operator, so if a code fails, check its help pages.

In the US, the per-call codes are written into federal rules. Carriers using modern signalling must treat *67 dialled as the first three digits of a call as a request not to pass the number on an interstate call, and must recognise *82 as a request to pass it when the line is blocked by default. They may not charge the caller for per-call blocking (47 CFR 64.1601).

Withholding it on every call

If you want your number hidden by default, there are two places to set it.

• On the phone. iPhones have a switch called Show My Caller ID in the Phone section of Settings. On Android, look in the Phone app's settings under Calls, Supplementary services or Additional settings for an entry named Caller ID, with choices such as network default, hide number or show number. The exact path changes with the manufacturer and the software version.
• With the operator. Some operators hide the phone switch and handle the setting on their side instead: through your online account, a code, or a request to customer service. Fixed lines and many internet phone services work this way too. In the US this is usually called line blocking.

Whichever you use, test it. Call a friend or a second phone and check what appears. A handset setting may not follow your SIM to another phone. When the line hides your number by default, the "show" prefix in the table above reveals it on a single call, which is useful when you ring a doctor's surgery or a friend who rejects anonymous calls.

What the law guarantees in the EU

The European ePrivacy Directive sets out the rights in a few lines. Where an operator displays caller numbers, it must let the caller prevent the display on a per-call basis, "using a simple means and free of charge", and the subscriber must also be able to do it for the whole line. The same article gives the person receiving calls three matching rights: to stop their own phone displaying incoming numbers, to hide their number from callers when they answer, and, where numbers are displayed before the call is connected, to reject incoming calls whose number has been withheld (Directive 2002/58/EC, Article 8). The per-call right also applies to calls made from the EU to other countries.

That last point is worth knowing from both ends. If you withhold your number, some people and businesses will simply never hear the phone ring, because they have switched on anonymous call rejection. In the US many carriers offer the same service, commonly activated with *77; your operator's support pages list the code it uses.

Who still sees your number

Withholding works against the person you call. It does not work against the network, and several kinds of call are deliberate exceptions.

• Your own operator. It must know who is calling to connect and bill the call, and it keeps that record. Withholding changes the display, not the records.
• Emergency services. Both legal systems exempt them. The US rule does not apply to 911 calls and emergency lines, and the EU directive lets operators override withholding, line by line, for recognised emergency organisations such as police, ambulance and fire services. If you call 112 or 911 with your number hidden, they still get it, which is what you want. Our guide to emergency calls over VoIP and Wi-Fi calling covers how location is sent as well.
• Toll-free numbers. In the US, the terminating carrier must respect the privacy flag unless the called party subscribes to a service based on the caller's billing number and is paying for the call, which is exactly how freephone lines work. A business with a toll-free number can therefore receive your number even when you dial *67.
• Nuisance call investigations. The EU directive allows operators to override withholding temporarily when a subscriber asks for malicious or nuisance calls to be traced, and the US rule makes an exception for legally authorised call tracing requested by law enforcement.
• Text messages. CLIR applies to voice calls. An SMS always carries the sender's number, and none of these codes hides it.

There is one obligation going the other way. In the US, anyone making telemarketing calls must transmit caller identification and is prohibited from blocking it, so a sales call showing "No Caller ID" is already breaking the rules.

Calling apps, Wi-Fi calling and business lines

Carrier Wi-Fi calling uses your ordinary mobile number and normally follows the same caller ID setting as calls over the mobile network, but a quick test call over Wi-Fi is the only way to be sure. App-to-app calls on messaging services are a different system: the other person sees your account, which may include your phone number, your username or both, according to the app's privacy settings rather than the network's. Look for a setting that controls who can see your phone number, and remember that in many apps people who already have your number saved will see it regardless.

Business phone services often let you choose which of your own numbers appears on outgoing calls. Displaying a number that is not yours is spoofing, whatever the software allows.

When a withheld call rings your phone

A withheld number is not a scam in itself: doctors, hospitals and police officers often call with their number hidden. Still, never give codes, passwords or card details to someone who called you; if they claim to be your bank, hang up and call the number on your card. If you would rather not take such calls at all, turn on your operator's anonymous call rejection or the phone's filter for unknown callers. And never return a missed call from an unfamiliar international number just to find out who it was; our guide to one-ring scams explains why that callback can cost you money.

A short checklist

1. For one call: #31# on most mobiles, *67 in North America, 141 in the UK, followed by the number.
2. For every call: the Caller ID or Show My Caller ID setting on the phone, or your operator's line setting.
3. Test with a second phone, and test again over Wi-Fi calling if you use it.
4. Use the "show" prefix for people who reject anonymous calls.
5. Expect your number to reach emergency services, toll-free lines and your own operator anyway.
6. Withholding hides a number; it never makes a call untraceable.

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