Pulse Monitor app
The Pulse Monitor is claimed to monitor oxygen saturation and heart rate. It shows real-time pulse graph and provides reminder to measure your oxygen saturation and heartbeat periodically. However, this app only works with a built-in sensor on Samsung devices.
Instant Heart Rate HR Monitor Pulse Checker app
This app is claimed to accurately measure pulse and heartbeat rate. The app is cited to function similarly to a pulse oximeter and monitor blood circulation and heart rate training zones. It shows PPG graph and comes with Google Fit support.