The wristwatch key This gun broadcasts radio frequencies. If a wristwatch transponder — activated by a PIN number — is adjacent to the gun, the watch will return a signal to unlock the gun. The fingerprint key Guns equipped with a fingerprint-recognition system on the grip can be fired only by authorized users. Fingerprint sensor A red light indicates the gun is locked and unable to fire. A green light on the gun signals that it is ready to fire. In this instance, only the middle finger of the left hand will unlock the weapon. Should an unauthorized person try to use the gun more than twice, the firearm will shift into high-security mode, requiring extensive steps to unlock it.

SOURCE: Justice Department.