Dropdeadkick: I was thinking the same thing. I am going to order some reed switchs and some hall effect sensors to play with. My concern is that I have some 110vac in that general area that might cause some issues. But I do intend to try.
Cr0sh: as the cap is put on and off it changes the travel slightly. You won't know its going too deep until the switch stops working..... but if you make it any shorter intially it won't trigger the switch.