Ever since my brothers honda got stolen, I have been racking my brain for some kind of cheap hidden kill switch. I created one that knocks out the fuel pump and it cost me 3 bucks. If some one wanted to steal it, they would have to tow it or do a LOT of work to get to the fuel pump. The switch is visible but anyone who saw it would not know what it is or how to operate it. It's only temporary, I found a much better way here...

Simple Ignition Kill Switch

You place a magnet on some secret place that you have selected and it activates a hidden switch. You can release the magnet and start your engine as normal. You could keep a magnet on your key chain, or hell, leave it in the car, what thief would think of doing something as crazy as rubbing a magnet around a car interior.

Anyone see any flaws here?