A campaign has been launched to raise awareness of how to call 999 when you are too frightened to speak out loud.
The Independent Office for Police Conduct watchdog warns it is "not true" that a silent 999 call alone will automatically bring help.
Around 5,000 of the 20,000 silent 999 calls made daily are put through to an automated system.
Callers are then led through a series of prompts and asked to press 55 to confirm there is a genuine emergency.
The system has been in operation since 2002 but police say many callers don't understand, or use it correctly.
As 55 was not pressed, the call was terminated and Devon and Cornwall Police were not notified of Kerry's call.
"Make yourself heard by coughing, tapping the handset or - once prompted by the automated system - by pressing 55.". »