Casio G-Shock GSW-H1000 User Manual page 39

Caution
The data from each sensor is used to estimate whether the watch is worn
on the wrist, and your heart rate is measured when it is detected that the
watch is being worn. If you do not want to measure your heart rate while
you are wearing the watch, select "OFF" for the "Detect wear on the
wrist"* setting. Note, however, that if you are performing a measurement
operation using a CASIO activity app, measurement is performed
regardless of this setting.
* To display the "Detect wear on the wrist" setting, swipe the watch face
screen downwards. On the screen that appears, tap the following in
sequence: D > "Accessibility" > "Heart Rate Measurement".
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