system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Does my phone check every second to see if the current time matches the time of a previously set alarm so it can trigger that alarm? How are these scheduled events generally triggered?
gpt
Your phone is literally just a computer. Computers have a piece of software called a scheduler. Schedulers are a fundamental part of the operating system and do way more than simply check for your alarms. They coordinate all of the other software that wants a piece of the main processor's time.

So, the scheduler has a list of all of the things that need to happen. If you are browsing a web page while also listening to music then the scheduler allots time on the CPU for each of those tasks.

It will also check to see if there are things that need to happen in the future. If a piece of software is set to wait for 1 second before checking on something then it will tell the scheduler that it needs CPU time in 1 second. Similarly, your phone's alarm will be set into the future and the scheduler will notice when the current time matches the alarm time.

Since the scheduler is always running and always making sure that things happen on time, an alarm is one of the easier things for it to do.