How do magnetic switches work?

http://en.wikipedia.org/wiki/Hall_effect_sensor <—- this is how they work, I use them all the time. You can also use a magnetic reed switch. If metal is your target then a prox switch will work: http://en.wikipedia.org/wiki/Proximity_sensor

Thanks @ARE_you_kidding_me! I want it to be as inexpensive and reliable as possible. Think the prox switch is a better direction to explore? When it’s a half in from steel I want it to switch on and when it’s farther away I want it switched off.

Magnetic switches are off or on when energized by a magnet.

Not a piece of steel.

Security switches are tripped by a magnet, opening and closing a door

For just a simple switch does it have to be contact free? What exactly are you trying to accomplish?

The typical magnetic switches commonly seen on doors and window consist of a magnet side and an internal reed switch. Radio shack sells them.
If you want something special you can buy your own magnet and reed switches from DigiKey.

It’s for a temporary battery powered light up sign we want to be able to throw up on the side of my cousin’s food truck at night. It’s battery powered with lights and a spinning donut made of foam. We wanted to put some rare earth magnets in the base so we could just quickly add/remove it and thought if we added a magnetic switch it could also trip the lights and motor.

While that might be fun to do is it really practical? Why not use a three dollar switch from Home Depot?