Block Unknown Numbers vs. Block Calls Not in Your Contacts
On Android these two settings sound identical, but they do very different things — and mixing them up is the single most common reason "blocking unknown numbers" doesn't stop your spam.
If you turned on "Block unknown numbers" in your Phone or Samsung settings and the spam kept coming, you're not doing anything wrong. That setting simply doesn't mean what most people think. Here's the difference, and how to actually block every caller you don't know.
The key difference
"Block unknown numbers" (the built-in setting)
This blocks only calls with a hidden, withheld, or private caller ID — calls that show up as "Unknown," "Private," or "No Caller ID" with no number at all. A telemarketer or scammer calling from a normal-looking (often spoofed) number still rings through, because their number is displayed.
"Block calls not in my contacts"
This blocks any number that isn't saved in your contacts — whether the caller ID is shown or hidden. It's the broader, more useful filter for everyday spam, since almost all spam shows some number. Stock Android has no single toggle for this; you need Do Not Disturb tricks or a call-screening app.
Why your spam still rings
Modern spam and robocalls almost always spoof a real-looking number — often a local one — so the caller ID is present. To the "Block unknown numbers" setting, that's a perfectly "known" (displayed) number, so it lets it through. Only a tiny fraction of spam hides its caller ID. That's why the setting feels broken: it's working as designed, just not on the calls that actually bother you.
The two settings side by side
| Incoming call | "Block unknown numbers" | "Not in contacts" |
|---|---|---|
| Saved contact | Rings | Rings |
| Number shown, not saved (typical spam) | Rings (not blocked) | Blocked / silenced |
| Hidden / "No Caller ID" | Blocked | Blocked / silenced |
| Stops everyday spam? | Mostly no | Yes |
| Built-in single toggle? | Yes | No (needs DND or an app) |
How to block every number not in your contacts
Since Android 10 there's a call-screening role that lets an app filter incoming calls by the rule "not in my contacts" — the contacts match happens inside Android, so the app never reads your contact list.
- Install Block Unknown Callers from Google Play (free, no sign-up, no contacts access).
- Set it as your call-screening app in the system dialog.
- Choose Block (reject) or Silence (mute the ringer) for numbers not in your contacts.
- Add an allow list or repeat-call bypass for important unknown callers.
See the full walkthrough in our guide to blocking unknown callers, or learn how call screening works.
What about Do Not Disturb?
Android's Do Not Disturb can be set to "Allow calls from contacts only," which does mute non-contacts. But it also silences notifications and alarms depending on your setup, and you have to toggle it on and off through the day. A call-screening app applies the "not in contacts" rule to calls only, all the time, without muting everything else.
Free · No sign-up · No contacts access
Frequently asked questions
Why doesn't "Block unknown numbers" stop my spam calls?
Because it only blocks calls with a hidden or withheld caller ID. Most spam shows a (often spoofed) number, which the setting treats as "known," so it rings through. To stop those, block numbers that aren't in your contacts.
What's the difference between "unknown" and "not in contacts"?
"Unknown" means the caller ID is hidden — no number is shown. "Not in contacts" means the number is shown but isn't saved in your phonebook. They're different groups of calls, and most spam falls in the second.
Can Android block all calls except my contacts?
Not with a single built-in toggle. You can approximate it with Do Not Disturb (contacts only), or use a call-screening app that blocks or silences every number not in your contacts.
Does blocking non-contacts need contacts permission?
No. Android matches your contacts internally and only passes unknown numbers to the screening app, so it never requests contacts access.
Will people I know still get through?
Yes. Anyone saved in your contacts always rings normally. You can also add an allow list for specific numbers that aren't saved.