My favorite cheap spy-tech/weird cheap gadget seller, Brando, just announced a GPS jammer that plugs into a cigarette lighter. The description is sparse, but I am guessing it can be used to block navigation/tracking/logging systems that rental cars and company fleet vehicles sometimes use to keep track of drivers. It's $49 and I don't know if they are legal or not. Gobal Positioning System (GPS) Jammer
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. Come and hear Mark speak at the ALA conference in Chicago on July 1.