Boot Lace Handcuff Key
It was designed to have a near zero likelihood of detection, yet still have the capability to be rapidly accessed when required. This was achieved by engineering a unique covert hide-out key which is located seemingly far out-of-reach of a handcuffed captive.
Discreetly attached to the tip of your bootlace, this handcuff key does not seem to be within any useful proximity while handcuffed behind your back. But just bend your knee up sharply and it puts it right into your hands! This works whether standing, sitting, or prone. Grasp the device, and then return your foot to its original position; as your foot descends the lace unties, leaving you with a tethered handcuff key in your hand.