Daylight saving time (or not) & electronic devices

I was having a chat with a student in a different time zone the other day.
I’m in the UK, she’s in the US.
In the UK our clocks were moved back one hour on 30th October, in the US one week later on 6th November.
Except for certain US states who do not observe daylight saving hours - Arizona for example.
We raised a question and had no answer so I thought I would put it out here.
In the UK our computers, mobile phones and other devices all automatically change their time reading according to daylight saving or standard time.
How does that work in countries such as the US?
People in Massachusetts and Arizona and California all buy computers and electronic devices. Yet only in the first and last of those states do the clocks alter in spring and autumn.
How do the computers know whether to change or not?

Also …
I was told there is a groundswell of opinion in many US states to end daylight saving. If that happened, would there be another panic situation fearing that all computers would cease to function, much like the millennium bug caused panic that the world would suddenly stop when the year 2000 came?


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The time zone and time on you phone is modern phones is usually provided by the network provider though usually there is an option to switch that off and set the time zone using your phones location. Big brother is tracking you to make sure you are always on time. With computers I expect the time is just adjusted automatically based on the time zone you have selected in settings. I would have thought that if any states, countries decided to not observe daylight saving then they would just adjust the time zone data.

That is certainly my understanding and would normally done at set up. However when all our stuff came out of storage when we moved from the UK to France, I obviously changed the time/clock setting to reflect CET.


So your local setting will adjust for DST if its applicable.


As far as I know it would be the same for mobile devices.


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My phone figures it out on its own. My computer has a setting regarding daylight savings time. My BMW….not so much.

Unlike the UK, Canada has 6 time zones and the Continental US has 4 so as James and Toby have posted we set our electronic devices to the time zone we live in. One province(Saskatchewan) doesn’t change to DLST and the south east part of British Columbia is on Alberta time. Newfoundland is 1/2 hour ahead. So time is a Concept Not a Reality :clock1: :clock11: :clock6:

Yes my PugGot needs manual intervention as well !

Thanks all for showing my ignorance and giving me the opportunity to reiterate… there are no stupid questions only things you don’t know the answer to.


I am based in the UK and firstly I’d say I really wish we just stayed on British Summer Time all year around. For me there’s no advantage to changing the clocks and I’d rather have the extra daylight in the hour after I finish work. With the clocks as they are it’s dark when I start and finish work.
I have 3 clocks that don’t adjust automatically. The clock on my oven which is no surprise as it’s as it has zero smarts about it. There’s my motorbike, which funnily enough is now correct because I didn’t move that to summer time earlier in the year and there’s my car. I feel the car is least forgivable one… it has smart stuff like lane detection and attempts to read road signs (I say attempts because it’s not very good at it) but the clock is just a dumb clock.

I’m in Scotland and am just back from holiday in France.

On the ferry from the UK to France the ship was on French time which of course is always one hour ahead of UK time. However my phone, iPad and my wife’s iWatch remained on UK time until we got off the ferry and picked up the signal.
I have an ‘old fashioned’ watch so could adjust that so we knew the time.
I wanted to set an alarm as the ferry docked early morning and we didn’t want to sleep in. What time should I set the alarm for on my phone? Much head scratching over that one!
I had the same issue on our return ferry crossing but in reverse as the ship was on UK time and our phones etc on French time.

While we were in France the clocks changed. Not an issue as all the electrical things adjusted automatically.

However, in the caravan we have one of those radio contolled clocks that picks up a signal from the UK. I adjusted it manually to compensate for the one hour time difference in France but despite being in the south of France at the border with Spain, every morning it had adjusted itself back to UK time! Very confusing. I ended up putting it in a cupboard to avoid confusion.

I’ll need to learn Jim Croce’s ‘Time in a Bottle’. :joy:

Used to do that with my old double clanger alarm clock back in the day, especially when I need extra zeds after a heavy night ! :alarm_clock:

That idea has been floated here in the UK too many times, but they’ve never just gone ahead and done it. I wish they would. Daylight saving comes from a different era and is no longer relevant to the modern world, certainly not in the UK anyway. All it does is create confusion and mess with people’s body clocks.

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It’s the same here. About every 2 or 3 years some politician brings up not changing the clocks, then the debate starts all over again do we stay on Daylight savings time or Mountain Standard. They waste Millions doing studies and surveys and nothing changes.

Pretty much describes politicians in general, I think… :thinking:

I live in Arizona. On most devices (at least those sold in the US), there is a time zone setting for Arizona. If not that, there is a way to disable daylight saving time. Things like cell phones know your geo-location and set the time based on where you are physically located. So, in winter, if I drive from AZ to CA the time will adjust by one hour. But during the summer, when we are on the same time as CA, it does not.

There was a time, years ago, when I had to check to see if the time changes on devices were screwed up in Arizona, but that hasn’t happened in a long time.

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I’m looking forward to hearing that one Gordon. :wink:

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Thanks @VeloVagabond

To add a little colour to this, network provided time and timezone information has been part of the GSM specifications for some time (since the late 1990s)

The local date, time and local timezone is pass from the base-station to the handset as part of the connection. Of course, the base station is local and static so the timezone is always known based on its physical location. Of course that also relies on the mobile operator properly configuring this information, which they sometimes don’t do.

But the upshot is, if you have your mobile phone (cellphone) configured to use “Network Provided Time” then it should always have the correct time if it’s connected to the network as it should always have accurate local time plus timezone information.

For devices that don’t have a SIM (or eSIM) in them, most modern Internet connected devices will sync their date and time to the Internet using Network Time Protocol (NTP) and there’s a hierarchy of network time servers around the world which provide this to various levels of accuracy (known as “Strata”). There’s directories of them at the internet cluster of ntp servers

Of course, what they get from one of these servers will be a time relative to “Zulu” (or UTC) and it’s up to the device to adjust this to the local time zone. Some devices (like PCs) will attempt to do this by trying to estimate their location based on IP address or other info, but it’s usually required to configure this manually. If you buy a device, it may already be configured to the timezone of the country in which you purchase it.

If changes to the way locations handle timezone data happen, then the part of the code that deals with this needs to be changed. Such changes are normally known about well in advance and PCs, tablets, phones, and other devices will, typically, add the change as part of their standard update procedures. If you are interested in this, here’s an article discussing recent changes to the Linux “tzdata” package which handles these rules which notes, for example, amongst other things:

If you have a device that doesn’t get updates (e.g. a DSLR camera), then these will have minor issues in those timezones where the rules change.



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Err… Did someone post a ‘Daylight Saving’ thread without the obligatory trailer link? :roll_eyes: :rofl:


Forgotten that one. its got to be a good reason for keeping DST going ! :rofl:

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Growing up in Indiana I always felt blessed that the state did not utilize DST and our clocks never changed. Life was good. Then, a while back, our governor at the time pushed hard to go to daylight savings time. He had some large donors who wanted to golf later in the day.
Long story short, the change was made but not all counties agreed to the standard. Now we have counties on different time zones. When I traveled around the state for meetings, I always had to check to see what time zone the meeting location was in. Many meetings were disrupted because not everyone thought to check the time.
Progress, indeed!