... you might have to clean the batteries off.
I received mine yesterday and mounted them on my bike.
I spun the wheel and turned the crank, but the new sensors were not detected by my Edge 810.
After a bit of futzing around, I opened the battery cover and noticed a small dab of liquid where the battery would touch the contact. I assume it's some kind of protection from corrosion while the battery is in the sensor unused.
I wiped the liquid off, put the batteries back in the sensors, and they were recognized immediately.
david