Here’s a really cool project using RFID to simulate a door lock or identification system of some sort.
The design is fairly straight forward, a custom circuit board links the BASIC Stamp to the RFID reader, and is powered by 12v. When a valid card is recognised, it provides 12v output to a door strike, and buzzer for 3 seconds. When an invalid card is recognised, it pulses 12v to a buzzer only for 250 milliseconds 3 times in a row (see below for video demo). It also features a trigger input which when connected to ground will simulate a valid tag bring presented to the reader (this is used to “buzz” open the door from a remote location).