How to Block Unknown & Spam Callers on Android

A simple, privacy-first way to block or silence every call from a number that isn't saved in your contacts — without giving any app access to your contact list.

Spam and unknown calls are relentless: robocalls, scams, marketers, and numbers you've never seen. This guide shows the fastest way to block unknown callers on Android and stop spam calls for good, while still letting the calls you actually need get through. It uses Block Unknown Callers, a free app that runs entirely on your device and never reads your contacts.

The fastest way: block calls not in your contacts

Android (version 10 and newer) has a built-in call-screening role. An app with that role can decide what happens to an incoming call before your phone rings — but only for numbers that aren't already in your contacts. That's the key to blocking spam without handing over your contact list.

1. Install the app from Google Play Open Block Unknown Callers on the Play Store and install it. It's free and has no sign-up.
2. Set it as your call-screening app On first launch, tap to confirm in the system dialog. This is the only permission it needs — it does not request access to your contacts, messages, microphone, or location.
3. Choose Block or Silence Flip one switch on the main screen. Block rejects unknown calls outright; Silence lets them through to your call log but mutes the ringer so you're not interrupted.
4. Add exceptions (optional) Use the allow list and repeat-call bypass so important unknown callers — clinics, delivery, a new work number — can still reach you.
5. Check the log & stats Every handled call is recorded, so you can see exactly who was blocked or silenced and how many interruptions you've cut.

What counts as an "unknown" caller?

Any number that is not saved in your contacts. Anyone in your contacts always rings through normally — the app never even sees those calls, because the matching happens inside Android itself. Among unknown numbers you can narrow the scope further (for example, only filter international numbers that start with + or 00) and carve out exceptions.

Block vs. Silence: which should you use?

Won't I miss important calls?

This is the biggest worry with any call blocker — so the app is built with several safety nets:

• Contacts always ring — saving a number is the simplest guarantee.
• Allow list — add specific numbers or whole prefixes that should always get through.
• Repeat-call bypass — if the same unknown number calls back several times in a short window, it's let through automatically (urgent callers usually try again).
• Pause filtering — temporarily turn filtering off when you're expecting an important unknown call.
• History log — every blocked or silenced call is recorded, so you can always call back.

Why not just use the built-in block list?

Android's built-in blocking works number-by-number: you can only block a spam number after it has already called you. New spam comes from endless fresh numbers, so you're always one step behind. Blocking by the rule "not in my contacts" stops the entire category at once — including numbers you've never seen before.

Is it private? Does it read my contacts?

No. The app has no contacts permission at all and never requests READ_CONTACTS. Because Android only routes it calls from numbers not already in your contacts, the app never sees your contact list, let alone uploads it. There are no accounts and no cloud sync — your block history, stats, allow list, and settings all stay on your device.

Frequently asked questions