The unit consist of a cylinder with a spring-loaded piston, which drives a release pin. The cylinder has a valve on the top which controls the vacuum in the cylinder. You simply screw the self-timer in the cable release thread on the camera, arm it, and release the piston. The spring will drive the pin down, overcoming the vacuum in the cylinder. By opening and closing the valve you can set the delay time. At the end on the movement, the pin "shoots" with great speed and force, and this may possibly shake the camera. I do not know how useful the gadget is, but it is surely working well, made nicely, and is quite uncommon.

The self-timer comes in a plastic case.