I used to have a cheapish computers for each of my bikes that stayed on that bike, but now I have a single Garmin that I switch between all of my bikes (road, mtn, cx/commuter).

Between forgetting to switch between profiles when changing bikes, and forgetting to press "Start" at the beginning of every ride (who thinks to do that on commutes?), I no longer have any idea what my "real" odometer reading should be for any bike.

I used to use this data to keep track of how much I ride each bike, how many miles various components had on them, and as a matter of pride. My co-worker and I used to go for bragging rights for yearly/monthly mileages. Now I have no idea what any of that data is.

What I'd like is to have a simple odometer for each bike. It doesn't need to do anything at all other than keep track of miles or even just wheel rotations - I can do the math later. I don't need speed, avg, cadence or any of that stuff. It doesn't need to be wireless or anything fancy. I'll probably mount it somewhere out of the way, like at the bottom of the seat-tube near the bb. Small size, weatherproof and relatively cheap would be good.

Does anything like this exist?