Some HR monitors use a straightforward chest strap with sensors that hook up wirelessly to the smartphone application or a computer. Chest strap HR monitors have existed for a number of a long time. The American Heart Affiliation (AHA) suggests monitors with cuffs that fit in your upper arm, as https://modernsmarthealth.com/product/telehealth-accessories/health-monitors-telehealth-accessories/latest-accessories-latest-products/jiacom-22-42cm-large-adult-blood-pressure-cuff-for-arm-blood-pressure-monitor-meter-tonometer-sphygmomanometer/