A campaign has been launched to raise awareness of how to alert police if you are in imminent danger, but can't speak.
The Silent Solution system has been in operating in 2002, but it's thought there has been confusion over how to use it - with only 50 of 5,000 calls per day being pushed through the automated system.
Callers who need police but are unable to make a sound should call 999 and then press 55 on mobiles to signify they are unable to talk.
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The police watchdog is warning that those who don't use the system properly may be dismissed as accidental or hoax callers.
Now a poster campaign by the Independent Office for Police Conduct aims to debunk the myth that simply calling 999 and staying silent 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.
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"Make yourself heard by coughing, tapping the handset or - once prompted by the automated system - by pressing 55."
The 'how to' campaign is backed by the family of Kerry Power, who was killed by her ex partner in December 2013.
The 36-year-old had made a silent 999 call, but did not respond to the BT operator and therefore 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."
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However, the family said she had not been told to press 55.
The statement continued: "A short while after the call was made, she was strangled."
An investigation conducted into the police's response found that Kerry had been wrongly advised by a police officer that assistance would be sent.
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The campaign, titled Make Yourself Heard, is also backed by Women's Aid and Welsh Women's Aid, as well as the National Police Chief's 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."
Around 20,000 silent emergency calls are made in the UK each day, but only a quarter are transferred to Silent Solution.
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