How does a clock that has been disconnected from power for any length of time know what time it is when it is reconnected to electricity?


Just your average alarm clock with no connection to the outside world; just it by its lonesome. i recently had a power outage for an hour and the clock powered back on and had the time exactly right…and had me very confused. Thanks everyone!

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4 Answers

Anonymous 0 Comments

Does it have a backup battery in it?

Anonymous 0 Comments

Most clocks made since electronics were modernized with transistors instead of tubes have capacitors, they’re like simple batteries that hold a charge for a while that can take a very long time to dissipate. That’s why it’s extremely dangerous to take apart large complex electronics like old cathode ray tvs, or big old radios, even if they’re unplugged and have been sitting on a shelf for decades. The capacitors can still hold a deadly charge that could electrocute you, even to the point of death. This means they can also be used to keep an internal clock keeping track of the time without using the display, which would suck up energy fast from the capacitors.

Anonymous 0 Comments

NIST broadcast the atomic time every minute including the date and dst info if in effect. Your clock may have the ability to auto set its time to this signal.

Anonymous 0 Comments

Are you sure there’s not a battery in there as well? Plug in alarm clocks usually have a spot for a battery in case of power outage.

Another thing that’s possible is if the power came back on at midnight or noon. Then it would show the correct time, albeit flashing but still the correct time.