The top metal part of the band activates by tapping it, so you can switch to sleep-tracking mode (it recognizes sleep patterns automatically as you use it).
It uses bioimpedance to measure heart rate, not LED-based tech like other bands: it can measure temperature and galvanic skin response, too, much like the Basis watches.
The Up3 is shower-friendly, but can't be worn while swimming. It lasts 7 days on a battery charge. And its heart rate tracking measures resting heart rate, incorporating the results in sleep analysis.