ideal for battery powered systems. can control about 600 watts of power to load while providing full isolation and transient protection.
http://www.imagineeringezine.com/PDF-FILES/lowssr2.pdf
http://www.citycom.gr/electronics/downcircuits/84.zip
http://www.citycom.gr/electronics/projects/lightswitch/lightswitchen.htm
The door opens inserting an electronic card! Very useful also to access private parks, enable photocopiers, activate showers and night light in sport resorts shared between clubs.
http://www.nutchip.com/progetti/card/card_en.htm
http://ourworld.compuserve.com/homepages/Bill_Bowden/page7.htm#trigger.gif
The relay switches on as long as the correct card is in. Converts pirate-smartcards to pacific and legal use.
http://www.riccibitti.com/NUT_chips/card/card.htm
PC parallel port relay card
http://www.tuug.fi/~isaarine/electronics/rele/
http://www.mitedu.freeserve.co.uk/Circuits/Switching/soundsw.htm