I was intrigued to read this:
You are the victim of identity theft and the fraudster calls your bank to transfer money into their own account. But instead of asking them for your personal details, the bank assistant simply presses a button that causes the phone to produce a brief series of clicks in the fraudster's ear. A message immediately alerts the bank that the person is not who they are claiming to be, and the call is ended.
Such a safeguard could one day be commonplace, if a new biometric technique designed to identify the person on the other end of a phone line proves successful. The concept relies on the fact that the ear not only senses sound but also makes noises of its own, albeit at a level only detectable by supersensitive microphones.
If those noises prove unique to each individual, it could boost the security of call-centre and telephone-banking transactions and reduce the need for people to remember numerous identification codes. Stolen cellphones could also be rendered useless by programming them to disable themselves if they detect that the user of the phone is not the legitimate owner.