Police who received 21 silent 999 calls from an address responded “on blues and twos” only to discover a man trying to unlock his phone.
The man had dialled the number multiple times “as it’s stated online that if your mobile phone is locked that calling 999 would unlock it”, Fenland police wrote on Twitter.
Officers had first tried to call the number and sent a text message, but got no response.
They attended the address in Wisbech, Cambridgeshire, on Thursday night.
A Cambridgeshire Police spokesman said: “We do investigate every silent 999 call to ensure someone is not in trouble.
“However, 999 should only be used in a genuine emergency – and not to unlock a mobile phone.”
No further action has been taken against the caller.