In university I had an old Crown Vic that somehow didn't need keys to start. You'd just grab the ignition and twist it and it would work whether or not the keys were inserted. It also had a keypad on the outside so keys weren't necessary at all.

Had a couple friends decide I'd be OK with them borrowing it for 20 mins to go grab groceries or whatever, and more than a few occassions where it was parked in a different spot than I left it.