This manual press on the Up helps the app to know when you first lie down in bed, so it can measure how long it takes for you to fall asleep.

WSJ: A Health Monitor to Nudge You as It Keeps Watch

On the road, spares can even protect you from yourself, as in when you arrive at the hotel late and frazzled and fall asleep before remembering the nightly recharging ritual for cell phone and computer.

FORBES: Spare Batteries