One that's really hard to bypass involves using a plug-in type headphone jack. The ignition and/or start circuit goes through a jumper wire in the phone jack, and once it's removed, turning the ignition key has no effect. The female socket can be located in a hard-to-see place to hide its real purpose.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!