As my Polar bike computer is 10 years old, I bought a Garmin Edge 130 device. It came with a heart rate sensor, and I bought a speed sensor and cadence sensor separately. When I turned on the device, it quickly recognized the heart rate sensor, and after a while it also saw both other sensors. I went for a ride, but speed did not show up properly on my display.
When I came home from the ride, the ride was properly registered on Strava, but it turned out the speed sensor was registered as a cadence sensor. I removed it, paired it again, same result. After a few tries I could register the sensors as two speed sensors or two cadence sensors, but not as a speed sensor and a cadence sensor.
After a good night sleep, I did what I should have done right away: remove the battery from one of the sensors, then put it back in. A green light started to flash, and pairing went ok. Same for the other sensors. Now I have a cadence sensor and a speed sensor registered. Can’t wait to try them out.