This Android app connects to a Bluetooth Low Energy (BLE) heart monitor, stores the data in a database, and plots in real time or from stored data. It reads and displays both RR interval values (RR) and heart rate (HR). Most heart monitor apps only do HR. There is much more information in the RR intervals.
See https://rawgit.com/KennethEvans/BLE-Cardiac-Monitor/master/app/src/main/assets/bcm.html
More information
More information and FAQ are at https://kennethevans.github.io as well as more projects from the same author.
Licensed under the MIT license. (See: https://en.wikipedia.org/wiki/MIT_License)