^^
Electronic devices often have a smaller secondary battery for timekeeping, just as a computer has its CMOS battery to keep the clock going when it is unplugged.
I think my nextel transmits its time. Because when my signal is out of range, it’ll be 12:15. Then when the signal comes back, all the sudden it’ll jump to 12:30.
I doubt if there’s any single answer to this; there are a number of solutions, such as:
-Although the phone battery may not hold sufficient charge to fully operate the phone, that doesn’t make it actually ‘dead’ - there will still be plenty of power left to run a hardware clock.
-Some phones probably have a smaller independent power source for the clock, that charges itself up from the main battery when it can.
-Some probably don’t care - the “remove the battery completely and your phone clock needs resetting - sorry” approach.
I think there are actually now CMOS clock devices with their own backup power built in, but the most likely answer is the first one; the phone says that the battery is dead because there isn’t enough juice to run the transciever, the screen, the illumination of the keys, the speaker etc, but there is ample residual power left to maintain the clock.
My Panasonic GD-something has a small battery similar to those found in watches. I know this because I disassembled it some time ago in order to paint it black.
Also, Mangetout is right. My older Nokia 3210 would keep the time even when the battery was seemingly “dead”. But if I removed the battery completely, it would lose the time within 30 seconds.
ParentalAdvisory, my phone also gets the time through the ether by some magickal spell. The nice thing is that it automatically resets itself if I cross time-zones. The thing that sucks is that if it’s completely in a no service area, it won’t tell me what time it is either - just shows a “Looking for Service” message.
FTR, I have a Kyocera from VirginMobile.
Cell phones get the time from the tower, not from an internal clock.
Some do, others don’t.
At least the nokias usually have the option to program the time yourself or else have it updated automatically
From Radio Controlled Clocks:
While I was investigating buying an atomic radio controlled wall clock, I’ve read that sometimes, it can be dicey in picking up the signal from Colorado. And so, I thought, why doesn’t someone make a clock that picks up the time from a local cell phone tower? According to the above quoted paper, such devices do exist. And yet, after a long and tedious search on the net, I haven’t found one. (And damn all those vendors who advertise a ‘radio controlled’ clock without mentioning ‘atomic.’)
My Sprint PCS phone obviously gets its time from the cell towers. It’s always correct to within two seconds of the Colorado atomic time, and it automatically changes time when moving through time zones.
Peace.
See http://www.endruntechnologies.com/frequency-standard-rackmount.htm
You didn’t say it had to be cheap :).
Actually, these systems can be economical when compared to cesium/rubidium/GPS.
An honest hats off to you. I usually pride myself on web search proficiency and you found something I couldn’t.
Now, ten extra Bozo bonus points to someone who can find a clock with a digital or analog display that uses cellular tower signals for calibration.
Anyone want to go into business selling one? Lot’s of discarded cell phones around for parts.
Peace.
I have a Sprint phone and have had a Verizon, both get the correct time from the network. I don’t think there is any provision to even set the time on the Sprint phone as it’s digital only. My T-Mobile phone has to rely on an internal clock that must be reset after a while.
moriah, I think it’s an answer to a question no one asked… well except for you. There are already clocks and wristwatches that get the correct time from the atomic clock in Colorado. Why reinvent the wheel?
Most cell phones get the time from the tower, that’s why there’s no need for you to reset it when you change time zones.
The question no one asked though, is why none of the phone book and call history information isn’t lost when the battery goes dead.
This info is stored in a type of flash memory, no? (Similar to CF cards in digital cameras, which don’t require power to retain data.)
Mine seems to do both. Like another poster said, if I go from an area with no signal after a long while to an area with signal, (and I’ve had a dead battery in the no signal zone) my clock might jump ahead a couple minutes.