Android
Block Unknown Callers Automatically auf Android
Android can automatically reject calls where no number or caller ID is transmitted. This covers calls from blocked or withheld numbers, and often catches spoofed spam calls that arrive without valid caller information.
The setting lives inside the phone app itself, not in the general system settings. Go to Tap on Phone ➔ Open the Menu ➔ Tap on Settings ➔ Tap on Blocked numbers ➔ Enable or disable Unknown. Once enabled, any incoming call with no displayed number is silently rejected before your phone rings.
What this filter actually catches
Only calls with a completely missing or suppressed caller ID are blocked. Calls from real numbers that you have not added to your contacts still ring normally, so this is not a general spam blocker.
When to use a different fix
If you are getting spam calls from visible but unfamiliar numbers, this filter will not help. In that case, a carrier-side spam protection service or a dedicated call-screening app is the better option.
Side effect to keep in mind: some legitimate services, like certain doctors offices, banks, or PBX systems, transmit calls without a caller ID. Turning this filter on means those calls get rejected too, without any notification that you missed them.