Some complain about no battery back up, but you don't need it as it saves your settings to memory (even when you lose power).

Yes, the "emergency power" mode works; I unplugged the unit and moved it around several times and it stayed on.

Power/"super capacitor":

When it does lose total power the atomic clock signal does reset the time.

For some reason it does not have a space where you can put some lithium batteries so that if your power goes out the alarm will still go off

If there is a longer power outage during the night, well, power outages set off an alarm in our security system, so I'll just get up and set the alarm on my iPod to wake up.

Otherwise, it's very accurate and at the times we lost power, I never knew it based on it's battery backup and atomic clock sync.