My personal favorite off the shelf switch, the Conceptus Tongue Switch is a long lasting mouth triggered shutter release system.
The Tongue Switch is comprised of a 1/2 inch pressure-sensitive switch mechanism, a 1 inch flattened and bite-resistant stem, a 36 inch coaxial wire, and a 2.5mm plug with a 90 degree elbow bend. It is configured so that the pressure-sensitive switch face is always oriented towards the user’s tongue, regardless of the direction of insertion into the mouth, thus allowing the wire to be routed to the left or right.
The tongue movement required is most similar to that of pressing bubble gum against the back surface of the front teeth before blowing a bubble. The user will feel a “click” each time the switch is depressed, indicating that a photo has been taken. The entire switch assembly is waterproof, and since it is situated entirely within the mouth, no jaw or teeth movement is required to retain or actuate the switch while taking photographs. This allows the Tongue Switch to be used with tight fitting rear-entry helmets and ratcheting chin-cups. This feature makes it the favorite of professional freefall photographers who insist on a perfectly stable camera platform.