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A campaign aims to raise awareness of a method of alerting police if you are in imminent danger but need to keep quiet.
The Silent Solution system, which prompts 999 callers to press 55 on mobiles to signify they are unable to talk, has been in operation since 2002.
But the instruction is only detected in about 50 of 5,000 calls a day pushed through the automated system.
The police watchdog says those unaware of the method could be assumed to be accidental or hoax callers and cut off.
The Independent Office for Police Conduct is launching a poster campaign, backed by a how-to guide, aimed at "debunking the myth" that a silent 999 call alone will automatically bring help.
Regional director Catrin Evans said: "It is always best to actually speak to a police call handler if you can, even if by whispering, but if you are putting yourself or someone else in danger by making a sound, there is something you can do.
"Make yourself heard by coughing, tapping the handset or - once prompted by the automated system - by pressing 55."
The campaign is being supported by the family of Kerry Power, 36, who was killed by her ex-partner in Plymouth, in December 2013.
She had made a silent 999 call but did not respond to the BT operator and so was transferred to Silent Solution.
A family statement said: "Although she was not able to speak for the fear of alerting the intruder to her actions, she followed the advice given by a police officer during an earlier visit."
However, the family said she had not been told to press 55.
"A short while after the call, she was strangled," their statement added.
David Wilder, 44 at the time, was jailed for life.
However, the subsequent investigation into the police response found Miss Power may have been wrongly advised by a police officer about when assistance would be sent.
Ms Evans said the inquiry identified a "lack of public awareness" about the method of alerting police that "could potentially save a life".
The Make Yourself Heard campaign is being backed by the charities Women's Aid and Welsh Women's Aid, and the National Police Chiefs' Council.
Lucy Hadley, from Women's Aid, said: "We need to look at all ways we can raise awareness and make the system work better for the people it's designed for, which are people in extreme distress and fear, and might not necessarily remember everything... on a poster or advertising campaign."
About 20,000 silent emergency calls are made in the UK each day.
A quarter are transferred to the Silent Solution system by handlers unsure whether they are genuine because they have received no response after 30 seconds.