Left mine idling at a Dodge dealership once for 3 hours (of all the gin joints...

). It wouldn't have been bad except for the defroster on full blast and the wipers going. Needless to say I got to test-drive the Dodge 2500 Cummins that my father was going to buy... i drove home and got the keys.
Ever since then I've kept the spare key in my pocket. I always drive around with both... just in case.