Fingerprint reader
Invented by Palle R Jensen
US Pat. no. 4,784,484

Background:
Every person on this earth has 10 unique fingerprints, even twins.
The fingerprint contains a number of characteristic points (minutiae) where lines split or merge.
A cheap, rugged and reliable method for reading a persons fingerprint has a lot of applications:
This invention describes a inexpensive fingerprint reader without any moving parts.