Heart Rate Monitors: Chest Strap vs. Watch

A heart rate monitor shows how hard your heart is working in real time. Used well, it keeps easy days easy, tells you when you have recovered between intervals and shows long-term progress in your resting heart rate.

Types of heart rate monitors

Type	How it measures	Strengths	Weak spots
Chest strap	Electrical signal of the heart (like a one-lead ECG)	Most accurate, reacts instantly to changes, good for intervals	Must be moistened and worn snugly; can chafe
Smartwatch / fitness band	Optical sensor (green light) on the wrist	Always on, tracks resting HR and sleep, no extra device	Lags during sprints; can be fooled by arm movement, cold skin, tattoos, loose fit
Armband (forearm/upper arm)	Optical sensor on a bigger muscle	More stable than the wrist, comfortable	Still optical, slightly delayed
Smart ring	Optical sensor on the finger	Good for resting heart rate and sleep trends	Not designed for workouts
Blood pressure monitor / pulse oximeter	Pressure waves / light through the fingertip	Good spot checks at rest	Not for exercise; may miscount irregular rhythms

How accurate are they?

At rest and during steady exercise, modern wrist devices are usually within a few beats per minute of a chest strap. Errors grow with sudden intensity changes, weight training, cycling over bumpy ground and anything that moves the watch on your wrist. A classic error: during running, the optical sensor locks onto your step rate and shows 160–180 "bpm". If a number looks implausible, check it by hand or with a strap.

Several smartwatches can also record a single-lead ECG and alert you to a possibly irregular rhythm suggestive of atrial fibrillation. These features can be helpful, but a notification is not a diagnosis — have it checked by a doctor.

Using a monitor for training

Set your zones from your maximum heart rate (220 minus age, or a tested value). See heart rate zones.
Keep easy runs easy. Set an upper alarm, for example at 70–75% of your maximum, on recovery days.
Recover between intervals: start the next repeat once your heart rate has dropped to about 65–70% of your maximum.
Watch heart rate recovery: how many beats your heart rate falls in the first minute after hard exercise. A drop of more than 12 bpm is generally a good sign; bigger drops come with better fitness.
Track resting heart rate: a morning value 5–10 bpm higher than usual is a common sign of illness, poor sleep or overtraining — a good day to go easy.

Choosing a heart rate monitor

For interval training, racing or anyone who wants precise numbers, a chest strap is still the gold standard; most pair with watches, bike computers and phone apps via Bluetooth or ANT+. For everyday health tracking, resting heart rate and sleep, a watch or ring is more convenient. Look for a comfortable fit, water resistance if you swim, and an app that lets you export your data.

No monitor? No problem

You can count your pulse at the wrist for 30 seconds and double it, or tap along with our tap-to-measure tool. During exercise, the talk test is a good substitute for zones.

This page offers general information, not medical advice. If your heart rate worries you, please talk to a doctor. In an emergency, call 911 (US) or your local emergency number.