Suggestion:
Do not track "sleep" if no HR is detected.
Application:
Currently, I wear my watch in the night to track my sleep time. In the morning, I take off my watch to have a shower. Garmin will think I am "sleeping" during the shower - as the watch is not moving (it's laying on a cupboard).
I think it would be useful if the algorithm assumes a person is not sleeping if no heart rate is detected.