Why Does Garmin Connect Show Missing Heart Rate Readings During Sleep?

When wearing a Garmin® watch that features an optical heart rate (OHR) sensor to bed, the device can lose track of your heart rate if it is pushed against the skin, compressing the area underneath the watch. For example, lying on your arm during sleep can result in 'unmeasurable' sleep to be displayed. Based on the algorithm used by your device, the act of compressing your device can cause your device to think it is no longer on your wrist. More consistent heart rate readings during sleep can be detected if the wrist where your watch is located is not compressed during sleep.

For more tips on heart rate accuracy for your watch see the section titled "Proper Fit of the Watch" from the following FAQ: Garmin Watch Optical Heart Rate Accuracy Tips.