ANY magnetic stripe card that uses the same standard will open the ATM doors. The switch is there to sense a card and performs no verification. It doesn't even connect to any net work.

This is a known fact as some crooks now load hotel room key cards with stolen credit card numbers. These cards then have the CC info on the magnetic stripes and machines will not be able to tell the difference (The plastic can still say "Holiday Inn").

Magnetic key writers are available on sale on the Net... just do a search on any search engine. You will be surprised how careful you have to be with your credit card numbers these days.