How accurate is Apple Watch in bed?

Comparison with a chest strap HR-monitor

July 16, 2019 - Willem L. Middelkoop

Sleep monitoring is a popular feature of many smartwatches and wearables. Devices like Fitbit, Withings, Apple Watch and Biostrap analyse biometrics during your sleep. These wearables are worn on the wrist and use optical sensors to capture your heart rate. I wondered how the optical sensors would compare to a high resolution chest strap HR-monitor.

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Wahoo TIKR (left) captures more data per minute than Apple Watch (right) per hour!

Combining heart rate measurements with movement data from a gyroscope sensor

Wahoo TICKR uses conductive pads in its strap to capture your heart's electric activity directly

Apple Watch uses an optical sensor to perform its automated heart rate monitoring

Heart rates measured by Apple Watch reveal that measurement is only done once every 5 minutes

Heart rate during my experiment night as captured with the optical HR sensor (top) and chest strap (bottom)

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