Be careful, in the larger lots they scan the license plates every day. I only know this because we forgot where our car was and they looked it up in seconds. So, potentially, they could map your license to your ticket on checking out.

Doesn't work at the airports where the ticket machine only gives tickets when there's weight of the car on the sensors beneath the roadway.

actually, they don't use weight, the sensors they use are inductive coils - so if you take a strong neodymium magnet and wave it above the coil it should hopefully trip it

http://www.wikihow.com/Trigger-Green-Traffic-Lights

Interesting, I had no idea. I did wonder how much trouble it would be to place sensors under the roadway; this makes for a much more elegant solution.

Used that exact trick to get an ex-girlfriend's car out of short-term parking in the old Denver airport where it had been sitting for two weeks. She went to her mother's funeral on short notice and didn't know she parked in the expensive lot...My roommate and I figured out that trick to save her hundreds on parking on her return when I went to get her car.