Android has three built-in ways to block unknown numbers, and which one works best depends on how aggressive you want to be

The simplest method is to let Android filter calls automatically. Open the Phone app, tap the three-line menu, go to Settings, then Call Screening. Turn on "Filter Unknown Calls" and Android will send calls from numbers not in your contacts straight to voicemail. You will not see a missed call notification, though the voicemail will still arrive.

If you want to see which unknown numbers tried to reach you before deciding whether to call back, use the Block List instead. In the Phone app Settings, find Block List or Blocked Numbers (the name varies by Android version and manufacturer). Tap the plus sign to add numbers manually, or long-press a recent call and select "Block" from the menu. Blocked callers will hear a message that your number is not accepting calls, and you will see a record of the attempt.

The third option is to use Do Not Disturb mode, which silences calls from anyone not in your Favorites or Contacts. This is less precise — it blocks known numbers too — but it is useful if you want temporary peace during work or sleep and do not want to manage a block list.

Key Takeaways

  • Filter Unknown Calls in the Phone app Settings sends unknown numbers to voicemail without showing you a missed call notification.
  • The Block List lets you see which unknown numbers called and manually block specific ones, giving you more control than automatic filtering.
  • Do Not Disturb mode silences all calls except from your Favorites and Contacts, but it blocks known numbers too.
  • Third-party apps like Truecaller and RoboKiller add spam detection and can block calls based on patterns, though they require permission to access your call history.
  • No method catches every spam call, and scammers regularly spoof local numbers, so blocking is most effective combined with not answering unknown calls.

Using the built-in Filter Unknown Calls feature

The Filter Unknown Calls setting is the fastest way to stop seeing unknown numbers ring through. Open your Phone app, tap the three-line menu icon (sometimes called a hamburger menu), and select Settings. Look for Call Screening or Call Filtering — the exact name depends on your Android version and phone manufacturer. Tap Filter Unknown Calls and toggle it on.

Once active, any call from a number not in your contacts will go directly to voicemail. You will not get a notification that someone called, and the call will not appear in your recent calls list. The voicemail message will still be saved, so you can listen to it later if you want. This is the least disruptive option if you rarely need to hear from new numbers.

One trade-off: legitimate callers — a doctor's office, a delivery driver, a recruiter — will not reach you. If you are expecting a call from someone new, you may want to turn this off temporarily or use the Block List instead.

Manually blocking specific numbers with the Block List

If you want to see which unknown numbers tried to call before deciding whether to block them, use your phone's Block List. In the Phone app, go to Settings and find Blocked Numbers or Block List. Tap the plus icon to add a number manually, or find a recent call from an unknown number and long-press it until a menu appears. Select "Block" or "Block Number" from the options.

Blocked numbers will hear a message saying your number is not accepting calls, and you will see a log of their attempts in your recent calls list (usually marked with a block icon). This gives you visibility into who is trying to reach you without silencing legitimate callers.

The Block List works well if you get repeated calls from the same number or if you want to block specific known spam sources. However, it does not stop new numbers from ringing through — you have to block them one at a time after they call.

When to use Do Not Disturb mode instead

Do Not Disturb mode silences all incoming calls except from people in your Favorites or Contacts. Open Settings, find Sound or Notifications, and look for Do Not Disturb. You can set it to turn on at specific times (like 9 p.m. to 7 a.m.) or set up it manually whenever you need quiet.

This method is useful if you want temporary relief from all calls — during a meeting, while sleeping, or when you are focused on something else. It is less precise than filtering or blocking because it silences known numbers too, so use it only when you do not expect important calls from people already in your contacts.

Using third-party apps for smarter spam detection

Android also allows third-party apps to filter calls based on patterns and databases of known spam numbers. Truecaller and RoboKiller are two popular options. Both apps analyze incoming calls against lists of reported spam and scam numbers, and they can block calls automatically or flag them for your review.

These apps require permission to access your call history and contacts, which is why they are more powerful than the built-in tools — they can recognize patterns across millions of calls. However, they also collect data about your calling habits. Read the privacy policy before installing to understand what information the app stores and shares.

Third-party apps are optional. The built-in Filter Unknown Calls and Block List handle most situations without requiring you to grant extra permissions. Use a third-party app only if you receive so many spam calls that manual blocking is not practical.

Why no method blocks every spam call

Spam callers use technology called caller ID spoofing to make their calls appear to come from local numbers or numbers similar to yours. Because the call looks like it is from a real contact or a nearby area code, it passes through filters designed to block "unknown" numbers. No blocking method can catch every spoofed call.

The most reliable defense is not answering calls from numbers you do not recognize. If the call is important, the caller will leave a voicemail, and you can call them back using the number from the message. Combining one of the blocking methods above with this habit will reduce the number of spam calls that interrupt you.

Frequently Asked Questions

Will blocked callers know I blocked them?

Blocked callers will hear a message saying your number is not accepting calls, but they will not receive a notification that you specifically blocked them. Some may try again from a different number.

Can I unblock a number after I block it?

Yes. Go to Settings in the Phone app, find your Block List or Blocked Numbers, and look for the number you want to unblock. Tap it and select "Unblock" or the delete option. The number will when ready be able to reach you again.

If I turn on Filter Unknown Calls, will I still get voicemails?

Yes. Unknown callers will be sent to voicemail, and their messages will be saved. You will just not see a missed call notification. You can listen to the voicemail whenever you check your voicemail app.

Do third-party call-blocking apps work better than the built-in tools?

Third-party apps can recognize more spam patterns because they access larger databases of reported spam numbers. However, they require more permissions and collect more data about your calls. For most people, the built-in Filter Unknown Calls and Block List are sufficient.

What should I do if a scammer spoofs my own phone number?

You cannot block your own number, but you can ignore calls that appear to be from yourself — no legitimate caller will ever call from your exact number. If you receive voicemails from your own number, you can report them to your carrier or to the Federal Trade Commission.