I got a bell from target, I think they are up to $15 now, but I think I paid $9 last year on sale. I upgraded to a wired cat eye with cadance, like $29 on sale at performance.
They are both auto on, and work just fine.
I like the idea of the geek stuff so I know everything I'm doing, but at the same time, I just see me running into the store and forgetting to remove it before someone else does, then there a couple hundred out the window...