Rhythm24 Notes

If trying to record a new workout causes the three indicator lights to blink yellow+red, then the memory is full. Either connect to the Rhythm app and download or delete the existing workouts, or hold down both buttons for 10 seconds to erase all of the stored workouts. (It looks like the Rhythm24 has a whopping 128K (K) of memory.)

Heartrate recording is 5 bytes per record - a 4 byte timestamp and a 1 byte data field.
Cycling recording is 12 bytes per record - a 4 byte timestamp, a 4 byte distance, a 2 byte speed, and 1 byte each for cadence and heart rate.

Total capacity - about 11 hours of mostly running, probably only a couple of hours of full cycling data.

The Rhythm24 won't appears as a heart rate monitor on Cyclemeter unless the Rhythm24 is in recording mode. Oddly enough, you can turn OFF the Rhythm24 recording mode and Cyclemeter will continue to record the heart rate data.

If the Rhythm app doesn't see the Rhythm24 device, the easiest fix is to delete the app and reinstall it.