Originally Posted by acrbill
Thats just internet folklore. If you knew how a car lock works you would realize how ridiculous that sounds.
Uhh it is not folklore. If you have a car with pneumatic power locks, the tennis ball trick works. The VAST majority of power locks are NOT pneumatic and never were. These days, I don't know of any modernmanufacutred car (at least in the US) using them.
There are several kinds of power door lock mechanisms, don't go assuming you have met them all.