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I just discovered that if I set the alarm clock and then power off the phone (by holding the power button and then selecting "Power Off") the alarm will still go off when the time comes.
Is this expected behavior? It makes me feel like "power off" doesn't actually power off the phone.
I have a Huawei Y530-U051 running android 4.3.
That is expected behavior. It allows you to turn the phone off if you need to ensure the battery doesn't drain (or whatever other use-case you can think up) and still have a usable alarm clock. It's not new, many Android devices do something similar, and every iPhone since the first-generation models also had that feature. I can also recall an old Nokia 3310 I had back in the early 2000's which did the exact same thing.
Turning the phone off does shut down the OS, so don't worry about that. Android supports the setting of "hardware alarms", which let the phone boot automatically at a predetermined time. Not every manufacturer included support for them, but yours obviously did.
Edit: The hardware alarm feature has been deprecated by Apple and isn't useable any longer.
On my Redmi 7, my Clock app Settings -> Additional alarm settings, has a feature Shutdown alarm, which I can disable so that the alarm does not go off after the device is powered off. It's a very useful feature, but I wish I had discovered it before my alarm woke me unnecessarily at 5:25AM, and not after. :-)
When the phone is turned off, it doesn’t mean that it is completely off. It is like in a sleep mode and the processor is still running a lower level system which does tasks like running the clock to keep the time correct, continuously monitoring the power button to know when to turn the phone on. As the clock is running and it is the alarm time , so the processor sends a signal to turn the phone on. Then the phone is turned on and the alarm rings.
Remember when you turned on your old mobile phone and you didn't have to set up the time every day again because the phone remembered what time it is?
It's not something of new, it's just that the phone starts a minute before the timer hits the alarm and it's build in because the phone requires at least 4 hours of recharge to last 10 hours of sleep in order to wake you up and not all customers have the possibility of having the wall charger or having the phone charged in their own room with a laptop in their own room.
However you can turn it off by clicking the small check button on the bottom of the screen when you turn the mobile off, so to say it, all phones hibernate on some level in case you don't happen to pull the battery off every time you want the phone closed completely.
