# self-setting clocks.. how do they work?

**URL:** <https://boards.straightdope.com/t/self-setting-clocks-how-do-they-work/40780>\
**Category:** Factual Questions\
**Created:** [November 11, 2000, 9:03am UTC](https://boards.straightdope.com/t/self-setting-clocks-how-do-they-work/40780 "2000-11-11T09:03:11Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![zuma](https://avatars.discourse-cdn.com/v4/letter/z/e9c0ed/32.png) [@zuma](https://boards.straightdope.com/u/zuma)\
**Post date:** [November 11, 2000, 9:03am UTC](https://boards.straightdope.com/t/self-setting-clocks-how-do-they-work/40780/1 "2000-11-11T09:03:11Z")

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I saw a commercial on late-night tv. it was a clock-radio thingie. it would self-set the time as soon as you plugged it in. and if the power went out, as soon as power was restored, it set the correct time again.

please explain. i figure it uses GPS, perhaps, to get the time. but then how does it know what time zone you are in? I just don’t know.

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**Author:** ![SterlingNorth](https://avatars.discourse-cdn.com/v4/letter/s/8dc957/32.png) [@SterlingNorth](https://boards.straightdope.com/u/SterlingNorth)\
**Post date:** [November 11, 2000, 9:23am UTC](https://boards.straightdope.com/t/self-setting-clocks-how-do-they-work/40780/2 "2000-11-11T09:23:34Z")

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If it’s a clock-radio, I’d assume it’d set itself based on an signal sent through the radio signal. However I’ve never heard of it before on a clock radio.

I do know that there exists TVs and VCRs that set the time automatically based on a signal sent through the data band of broadcast TV (that band that also sends closed-captioning info)…

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**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\
**Post date:** [November 11, 2000, 12:46pm UTC](https://boards.straightdope.com/t/self-setting-clocks-how-do-they-work/40780/3 "2000-11-11T12:46:57Z")

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I wonder if it’s one of the RDS radio things.  
These pick up information from local stations such as time.

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**Author:** ![DVous\_Means](https://avatars.discourse-cdn.com/v4/letter/d/9fc29f/32.png) [@DVous\_Means](https://boards.straightdope.com/u/DVous_Means)\
**Post date:** [November 11, 2000, 1:08pm UTC](https://boards.straightdope.com/t/self-setting-clocks-how-do-they-work/40780/4 "2000-11-11T13:08:10Z")

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It could be like my cheap bedside clock - it contains a nine volt battery to ensure that the time is not lost during a mains power outage. When mains power is restored, the correct time magically appears…:rolleyes:

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**Author:** ![Cabbage](https://avatars.discourse-cdn.com/v4/letter/c/f07891/32.png) [@Cabbage](https://boards.straightdope.com/u/Cabbage)\
**Post date:** [November 11, 2000, 1:18pm UTC](https://boards.straightdope.com/t/self-setting-clocks-how-do-they-work/40780/5 "2000-11-11T13:18:42Z")

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My dad has a clock like this, I believe it receives a radio signal from WWV (the shortwave time station out in Colorado) to set the time. I think he had to input what time zone he’s in, though I suppose one could be made that relied on GPS to figure that out.