Skype has announced that it will be adding an optional lie detector to its popular internet telephony service.

The 'KishKish' software attempts to determine whether the caller is telling a whopper by analysing the audio stream and checking for stress levels.

Lying evokes the 'fight or flight' response in humans, which makes muscles tense up, altering the pitch and tone of the voice.

"This is a really neat application, and the kind of thing we want to see more of," said Paul Amery, director of Skype's developer programme.

"Lie Detector is the latest in a variety of products in our premium Extras for Skype which greatly enhance the Skype communication experience."

The software was developed by Israeli software house BATM, and is already in use by the US military.

The software is available from Skype as a premium add on. No price or release date have been announced.