Biometric security systems usually on unique, unchangeable 'markers' such as fingerprints.
But Japanese scientists have identified another unique feature which can be 'read' by a biometric scanner - our rear ends, or, more specifically, the way we sit down.
The scientists have designed a chair which measures 360 pressure points to build a 3D profile of how a person sits - and it can identify who is sitting in it with 98 per cent accuracy.
The discovery could do away with car keys - and the researchers say it could even be used in offices instead of computer passwords.
The scientists, at Tokyo's Advanced Institute of Industrial Technology, say that the system is 98 per cent accurate.
It's a simple matter of fitting pressure sensors inside a normal car seat - so it could be in production cars as early as 2014.
The team says that the bottom-scan is actually less intrusive than other forms of biometric scans, such as the face recognition currently in use by UK passport control.
Most biometric systems require users to stand still to be scanned - whereas sitting is a natural instinct.