...or you could stash a cheap, disposable cell phone under the seat - something like the Motorola F3. There are various companies that allow you to track a cell

...or you could stash a cheap, disposable cell phone under the seat - something like the Motorola F3. There are various companies that allow you to track a cell number. Accuracy is roughly 30m radius (I think?). Then you just have to remember to keep the battery charged. One day someone will invent a simple dynamo-powered tracking device that accepts a standard SIM card...