A device for detecting contact pressure applied to a finger, the finger having a fingernail illuminated by light, comprises at least one photodetector for measuring a change in light reflected by an area of the finger beneath the fingernail in response to the contact pressure applied to the finger. The...http://www.google.se/patents/US6236037?utm_source=gb-gplus-sharePatent US6236037 - Finger touch sensors and virtual switch panels
