"When thieves cannot get access to secure properties, there is a chance that the thieves will stalk and assault the property owner to gain access. If the item is secured with a biometric device, the damage to the owner could be irreversible, and potentially cost more than the secured property. In 2005, Malaysian car thieves cut off the finger of a Mercedes-Benz S-Class owner when attempting to steal the car." -- Wikipedia
This was beautifully portrayed in Minority Report when Tom Cruise's character uses a pair of standalone human eyes (his old ones) to fool an eye scanner.
Image by Clearly Ambiguous