Timer to start up device while it's off

[Madmanda]

Hey. There's a timer in some computers that starts computer while it's off.
for example if I set a timer in my phone, I see it gets on and rings even if it's off (not locked), or there's an option in BIOS Setup to turn on PC with a timer. How does it works? is it PIT or ACPI or another chip that keeps track of time while computer is off?

[Octocontrabass]

How does it works? is it PIT or ACPI or another chip that keeps track of time while computer is off?

The chipset includes a clock that runs even while the computer is turned off. It uses standby power or the battery to keep time.