At mile 49 of a 54 mile ride, I noticed that my Garmin edge 810 was no longer displaying my current speed! Additionally, I was no longer getting power data from my PowerTap. However, I was still getting distance data. I pulled over and recalibrated the power meter. However when I resumed my ride I was still not getting any speed data. Eventually I noticed that the distance counter at stopped, so I pulled over again. I noticed that I did not have a magnet on the rear wheel. The rear wheel is new and came with the powertap hub. I guess I forgot to install a magnet on the new wheel. Regardless, the Garmin edge should have been able to give me speed and distance from GPS data. Anyway, after I got home I tested the sensors with a Garmin edge 705 I had lying around - with the same results. It appears as though the batteries in both the speed/cadence and PowerTap are good. I'm considering factory resetting the Garmin 800. Before doing so I just thought I'd check the forum for other ideas.