COROS Heart Rate Monitor, Comfort, Easy to wear, Auto-wear Detection, Advanced Sensor, Precise Data, Bluetooth, 38 Hours Battery Life, Connects up to 3 Devices at Once, for Run and Bike-Grey

My watch would often go into cadence lock and provide wrong HR data on easy to medium pace runs. This optical armband heart rate monitor from Coros seems to have resolved that issue. The heart rate data now coincides with the perceived effort. The band is pretty snug and comfortable and stays on the arm once strapped. It is an optical HR sensor with an inbuilt battery and, an advertised battery of 38 hours. The battery dropped by just 2% after a 3hr activity - battery life looks promising. Although it is basically just the same optical sensor on my Coros watch and does not come with any additional data or sensors. It would've been a nice addition if they'd included an HRV measurement or a thermometer.

This heart rate monitor is designed to be worn on the upper arm. It seamlessly synchronizes with the watch and has an automatic on feature. It is user-friendly and hassle-free.

This doesn’t even work don’t recommended