I have a question for all 510/810 owners out there…

I just got my 810 unit (bundle), and installed the cadence/speed sensor according to instructions. At first, my Edge unit wouldn’t pair up with either the cadence/speed nor the HR monitor. Upson screwing around for a few minutes, I realized the HR monitor has to be worn before the unit can detect it – ok, no problem.

However, the cadence/speed sensor would not pair up (tried restarting the unit several times to no avail). Thinking there was something wrong with the sensor (perhaps a weak battery), I decided to go out for a quick ride to test the overall operability of the unit (minus the cadence/speed sensor). When I got back home, I tried pairing up the speed/cadence sensor one more time, and this time it got paired up on the first attempt.

My question is: does anyone know why I had to go for a ride first before the unit would recognize the sensor? Will the sensor get picked up immediately on my next ride? Also, after having the bike sit in the garage for 24 hours following that first ride with the unit, the status light (red/green) on the cadence/speed sensor would not light up when spinning the wheels/pedals (in a stationary position).

Any other general info about how these sensors operate will be greatly appreciated.

Thank you in advance