A car insurer which introduced phone lie detectors says a quarter of all vehicle theft claims have been withdrawn since the initiative began.
Insurance fraud costs the industry £1bn a year
Admiral started using Digilog voice stress analysis technology in May, in an attempt to stamp out fraudulent claims.
When policy holders call, they are told they are being recorded and their voices are being analysed.
Customers are then asked general questions to identify normal stress levels in their voice before being asked for specific details of the incident for which they are claiming.
Where irregular stress levels are detected by the system, policy holders are called back and given the opportunity to withdraw claims.
An Admiral spokesman said: "We are extending the test for an indefinite period after 25% of theft claims referred through Digilog were withdrawn."
The company stressed that it did not mean all the withdrawn claims had been fraudulent, saying some may have been dropped as a result of stolen cars being found.
In August, banking giant HBOS announced plans to trial similar technology to try to beat fraudulent household insurance claims.
And Highway Insurance, part of the Lloyds of London group, has been using the Digilog analysis system on motor insurance claims for more than a year.
The Association of British Insurers estimates that fraud in household and motor insurance costs around £1bn a year.