Smart guns don’t have to be entirely new manufacture – some of the most interesting technology can be attached to an existing weapon. Identilock is a technology developed by engineer Omer Kiyani, who has a personal interest in gun safety from being shot in the face as a teenager. It takes the form of a piece of hardware that fits over the trigger mechanism of an existing handgun, with a fingerprint sensor on the side. If the correct finger is pressed to the reader, the hardware quickly unlocks and detaches from the weapon, leaving it ready to use. Unlike some of the other technologies on this list, it can accept multiple users.