A lie detector is being used to help detect benefit cheats by a north London council, which says it has prevented more than £100,000 in benefit fraud.
Software is being tested on housing and council tax benefit claims
The voice-risk analyser software has been monitoring phone calls to Harrow Council since May.
It detects minute changes in a caller's voice which can indicate when they may be lying.
But critics say analysing someone's voice alone is not an effective way to detect whether they are lying.
The technology is already used by the insurance industry, and the council is using it in a trial part-funded by the government.
It is being tested on housing and council tax benefit claims first, and is due to be used in job centres later this year.
The system first analyses the characteristics of a caller's "normal" voice to establish a benchmark. It then looks for changes in voice tone and frequency to identify signs that someone could be lying.
Benefits staff can then ask for further evidence to support any suspicious claims.
Griselda Colvin, Harrow Council's benefits manager, said some callers withdraw their claim at this early stage of investigation.
"Some people have willingly said 'OK I'm not going through with it, I'm withdrawing my application' and that's what we're looking for - those are the cases we're looking to identify," she said.
Changes in voice tone are detected to indicate someone may be lying
The council said the voice-risk analyser has already saved it £110,000 in benefit fraud.
But polygraph examiner Bruce Burgess said analysing someone's voice can determine whether they are stressed but it does not give an effective indication that they are lying.
"You don't know whether someone is stressed because they are lying, or stressed because they are angry, or stressed because they are embarrassed," he said.
In contrast the traditional polygraph lie detector carries out a more extensive test of heart rate, sweat and breathing.
"There is no evidence to show that the voice stress analyser gives valid results at all," Mr Burgess said.
Nevertheless the government plans to part-fund voice-risk analyser trials in a further five councils, including Birmingham.