NOOP
Pair your strap over Bluetooth, keep all data on your own device
...The app can read data such as heart rate, R-R intervals, temperature-related values, respiration signals, battery information, and events, depending on device support. It also imports WHOOP CSV exports, Apple Health exports, and nutrition CSV data to build a local history. NOOP computes metrics such as recovery, strain, HRV, sleep, workouts, trends, and correlations using transparent on-device analytics. It is an independent, unofficial interoperability project for users who want local-first access to their own wearable data.