noun
heart rate monitor; cardiometer watch
A device that measures and displays heart rate, often worn on the wrist or chest during exercise or medical monitoring.
ランニング中は心拍計で心拍数をチェックしている。
I check my heart rate with a heart rate monitor while running.
この心拍計はスマートフォンと連携できます。
This heart rate monitor can connect to a smartphone.
脈拍計 is a pulse meter, often used in medical settings; 心拍計 is more common for sports and fitness devices.
Compound of 心拍 (heartbeat) + 計 (meter, gauge). A straightforward modern technical term.