According to documents from Google, the feature is meant to sound an alarm and contact emergency services whenever the person wearing the watch loses their pulse. This could be from a heart attack ...

Once it detects a loss of pulse, it will make a good-faith effort to alert the user to ensure that it isn't a false alarm. If the watch detects no motion and the watch owner doesn't respond, the watch ...

The first-of-its-kind Loss of Pulse Detection feature on the Pixel ... If the user doesn't respond and no motion is detected, an audio alarm and countdown initiate. If the user doesn't respond ...