Polar's new fitness tracker constantly monitors your heart rate
 

Polar's latest fitness band called the A370 is a multi-tasker like the company's older wearables, and at $20 less than its predecessor, it's definitely the better choice. It monitors your heart rate every five minutes, whether you're resting or exerc...

https://www.engadget.com/2017/05/24/...-rate-monitor/