CuffMaxx High Security Handcuffs
The CuffMaxx is a "conversion" kit which can be used on a variety of cuffs made today (pictured is a Peerless Handcuffs kit). This kit will covert a pair of standard cuffs to a high security one.
The process is pretty simple, use the included tool to screw the four screws holding together two plates per cuff. These plates cover the cuff lock case without blocking access to the arm. Between the front plate and the cuff, there is a small driver (key nib) which is a truncated key. One side of the driver goes in the lock mechanism of the cuff - the other in the underside of the Medeco lock which an integral part of said front plate.
Once applied, the cuffs will still work as before except that they require the special included key to open. Medeco locks are nearly impossible to pick, certainly MUCH harder than a standard cuff lock. The cuffs can be double-locked as before, though the required pin is much longer. There is such a pin included in with the key.
The company also has an option to assemble the cuff for the user rather than sell the kit on it's own.