Garmins give more accurate speed, distance and auto-pause function using a wheel sensor as it helps compensate for GPS wander and recording granularity. A Bontrager Duotrap sensor we have here works with the Edge so I suspect the SpeedTrap sensor will work as well.
I see.. ok, I will try it out tonight on the bike. I actually have the Edge 800 and SpeedTrap with me right now. I stroke (back&forth) the magnet over the SpeedTrap and Garmin unit found it!! I hope the magnet will attach properly on to the bladed spoke. The one I got on my wheels are bladed spoke not the rounded ones.
Like was said, just use the speed trap - I just use the duo trap and it works great. the sensor that came with mine works fine on flat spokes. Make sure you enter your tire size if you want to have accurate readings though.