This post is about the older model of the Scosche armband HR monitor but this very well might apply to the newer Rhythm 24 monitor that took its place.
Up until recently I’ve been using the Scosche as a replacement for my Apple Watch (Series 3) HR monitor during workouts. It has better accuracy and updates at a much faster rate (once per second) than the Apple Watch. I’ve always paired it directly to the watch and have only used it with the Apple Watch workouts. But lately I have not been wanting to wear the Apple Watch and have been experimenting with other applications on my iPhone to see how that all works together.
The one piece of advice I have is to ignore what is written in the manual and don’t pair the Rhythm+ with the iPhone via Settings->Bluetooth. That step is completely unnecessary and seems to cause problems when trying to get the Rhythm to work with other applications. I experimented with multiple applications (Scosche’s own Rhythm Sync, Polar Beat, and FITIV Pulse) since each has their own pairing setup.
If I paired the Rhythm+ with the iPhone first, the pairing in each of the apps generally would not work properly. Sometimes it would pair, sometimes not. If I forgot the Rhythm+ in the iOS Bluetooth settings then paired the device individually with each app it worked flawlessly when I switched between applications. I’m not sure why Scosche specifically calls out pairing with the iPhone first in their directions but it certainly isn’t necessary and causes problems using the device.