My wife has a digital alarm clock that can reset itself after the power goes out (without battery backup) by whatever data is streamed along with our AC power. So, why can’t it auto-adjust to fall back to Standard Time and vice verse? She actually has to throw a toggle switch to make this happen without actually adjusting the time on her clock.
What? How can it be so advanced and so stone-age at the same time? 
Does anybody really know what time it is?
(Moving to General Questions)
You might get more replies if you get out of Chicago.
Are you sure there’s no back-up battery, like a button cell? I don’t understand when you say “…whatever data is streamed along with our AC power…”
According to the timestamp on the previous post, I am replying before it was posted. Must check personal settings on SDMB…
My guess is the data stream it receives is constant year-round regardless of whether Saving Time offset is implemented locally. So the operator has to tell it to apply a 1-hour (or other, if GMT) or not, and when.
Do you know what the time data stream source is?
what make and model of clock?
Darn, was anyone thinking clock in a car here?
Yeah, I was thinking that’s what an “auto clock” was going to be.
And I, too, was puzzled by “whatever data is streamed along with our AC power.” I didn’t know such a thing was even possible. So my best guess is that the OP is confused about how the alarm clock in question actually works, and that it actually does have battery backup or somehow saves the time in the event of a power outage. (My VCR does this, but has to be manually adjusted for DST.) But if the OP could specify the make/model of the clock, or even post a link to a description, we’d know more.
Long time listener, first time caller.
Jinx, can you give us a manufacturer and model number for the clock? I found several with similar features with a Google search, but didn’t deep dive any of the technology yet.
There is no such thing. It almost certainly has a shortwave radio receiver for the WWVB time signal broadcast by NIST: WWVB - Wikipedia
Since the US covers (and the WWVB signal reaches) several time zones, the WWVB signal sends out GMT. Each receiver must know its present time zone and apply the appropriate offset.
I’ve got a cheap Emerson Smartset alarm clock radio from Walmart that sets itself with the WWVB signal. I had to initially set it for CST when I bought it but since then it changes itself for every daylights saving time and back.
As others have said, the clock can’t know which time zone you are in based on the radio signal it uses. (And it is a radio signal). Even within a given time zone, it still can’t know daylight savings time. Arizona, for example, does not use daylight savings time.
At least you have a manual switch. The automatic-setting alarm clocks I have were designed to also auto-adjust for daylight savings time. They were programmed to adjust based on the old date, which was great for many years. However, the date for the change has been difference for a few years now which means I now have to manually adjust them twice as often. (Yes, I should just buy new ones, but I’m too cheap).
It is probably getting a signal from a time beacon somewhere and has a little battery which will keep the time for a short while if unplugged. No information goes through an AC line.
I think the toggle switch is a GREAT idea. We [del]have[/del] had an auto-clock that was fantastic… until stupid stupid people in US government decided it was a good idea to make DST longer. The clock still switches based on the OLD DST algorithm, which means we have to manually fix it. THEN a week later we have to adjust the time for the correct DST change.
Toggle switch.
Love it.
Embrace it.
Every clock should have it.
I have a clock like this. It is an Emerson Research CKS3029 clock radio. It sets the time automatically when plugged in (though you have to set the time zone the first time you use it, if you are not on EST) and recovers correctly after power outages. However, mine does know about daylight savings time, and it reset itself automatically this weekend. It also shows the day of the week, and according to the manual, it knows about leap years. The manual says the automatic adjustments will work through 2099.
I did have the impression from somewhere that it was picking up some sort of signal through the power lines, but looking at the manual again, I can find no mention of that. It does not really explain how it works, except for some mentions of its internal computer and rechargeable lithium battery. Could it all be programmed in in advance somehow? It keeps good time, anyway, I have never had to adjust it (unlike other electronic clocks I have).
I did not buy it for this feature, but I like it. I think it cost me under $30 (probably nearer $20) from Rite Aid.
The company web site is here, but it does not seem to have any information about how the “SmartSet” technology works.
After looking further at the manual, it appears that if it is unplugged long enough for the lithium battery to become exhausted, it will revert to 12a.m. on 01-01-2005, and will need to be reset manually to the correct date and time. From that I infer that they probably set up everything in its memory at the factory, give the battery a good charge, and then hope someone buys it before the battery runs out. It’s timing circuitry must be good.
i have clocks that receive time via radio signal and you set the time zone.
i have a clock that you set manually and use a switch to do the daylight time shift. i supply a backup battery.
i have a clock that was set at the factory running on the supplied backup battery. i set the time zone. it has current dates for time change and a 100 year calendar. leave plugged in when replacing backup battery to avoid manual time resetting.
Email me on New Year’s, 2100 and we’ll see if it works.