Electro magnet - Comes in many sizes and shapes, usually short or long oblong and round - Used for door access control and to keep doors held open, they are available from security shops and Amazon. This is our mark #1 and has a timer built in but you can use plug in timers like the type on our Remotes & Timers page. You can find more about them by searching Google for "magnetic locks for doors". As with our winches we tend to control them now via our logic controller as this gives use much more flexibility. We used this on our first ever shoot with Annalease and we keep using them for securing the girls or simply dropping keys into reach.