I got a jolly logic mini altimeter from Amazon. Quite cheap but effective. Logs the maximum altitude reached or it can give a real time read out (which you can put in the FOV of your camera, I guess). Weighs a couple of ounces only and charges through a USB port. I think it is a key fob thingy for mountaineers.
Thanks Clive.
After some thinking, I think I want full telemetry now. I think also having the exact coordinates could help recover the quad in case of a mishap.
Still, I might check into that for my other quad
How will you get full telemetry?
My bird usually starts flights in the woods, where the phone doesn't work anyway. I'm still searching for an extremely lightweight tracking device.