How do phones keep track off time while off and without internet connection?
In: Technology
There is a type of chip called a Real Time Clock which is specifically designed to use as little power as possible to keep track of time. It is usually connected to a tiny battery or even just a capacitor so that it can keep track of time even when the device is powered off and the main battery is out of power or disconnected. It can also be programmed to send a signal to the device to power on or at least wake up from deep sleep at certain times.
Even when your phone is off, there is still a very small circuit that is powered. This circuit, among other critical things, is keeping track of the current time. It consumes very little power, so it doesn’t drain the battery. Even when the battery says it’s dead, there’s enough charge left to maintain these low power critical functions.
Every computer device that keeps time will have a battery somewhere to help it keep time when its main power is gone. Even a desktop computer will have a watch-style battery on the motherboard to keep the circuit going.
One extra advantage that cell phones have is that, if they ever happen to go completely dead, they can set their time back via GPS. The way GPS works, satellites in known positions are broadcasting a signal that contains their time. If you get 3 pings and know the current time, you can figure out your relationship to those 3 satellites and it narrows it down to one point. If you can get pings from 4 satellites though, you can actually narrow down your position *and* the time from them. This is why phones have such accurate timekeeping.
They have a battery. When you turn the phone it’s not truly off, it still keeps track of the time. If you removed the battery it would forget the time.
To add to everyones explanation of an additional battery within, the same is true of PCs. The CMOS battery keeps just enough juice going to keep track of time, etc, while powered down. If you have ever looked at your motherboard and seen a circular watch battery on it, thats what the battery is doing.
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