London, Oct 19 (IANS): The iPhone 4 is so sensitive that it can decode what exactly is being typed on a computer keyboard and can double up as a spy phone.

People place their mobiles on work desks and these could be used by hackers to track what they write in e-mails or sensitive documents.

A Georgia Institute of Technology research team in the US discovered how to do it using a smartphone accelerometer - the internal device that detects when and how the phone is tilted.

They have found it can be harnessed to sense keyboard vibrations and decipher complete sentences with up to 80 percent accuracy, and the iPhone is best at it, the Daily Mail reported.

"We first tried our experiments with an iPhone 3GS, and the results were difficult to read," said Patrick Traynor, assistant professor in Georgia Tech's School of Computer Science.

"But then we tried an iPhone 4, which has an added gyroscope to clean up the accelerometer noise, and the results were much better. We believe that most smartphones made in the past two years are sophisticated enough to launch this attack."

The technique works by using mathematical software that detects pairs of keystrokes, rather than individual letters.