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I know that the alarm isn't working when the phone is turned off, but my question is: Why doesn't this work? What were the developers/engineers thinking?

I always used my mobile phones as alarm clocks and even very old mobile phone support alarm clocks when they are turned off.

gary
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RoflcoptrException
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    My old piece of crap Motorola v360 used to be able to do this, I think in Android the Alarm is running on top of the OS and not on a low level like these simpler phones. – mbwasi Jan 19 '11 at 15:34
  • You really mean off, like powered down, not just not connected to a cell network? – Amanda Mar 24 '11 at 00:15
  • I never turn mine off. I use Tasker to turn notifications off overnight, and if I really don't want calls, I use airplane mode. – TomG Oct 18 '11 at 01:38

4 Answers4

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There is no power to the phone when it's off. It's actually off. Some phones have a minimalistic charging mode that just shows a battery animation, but I have yet to see an Android device that boots into a clock-only type mode.

The Android OS is designed to use minimal power when not in use. If you have a problem with the battery dying overnight, it's probably due to a third-party app.

Matthew Read
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    Can it really not spare the amount of power required to run a digital watch for three years on a tiny button battery minus the overhead of the LCD screen? – mattdm Jan 15 '11 at 03:17
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    I'm sure it can, but most Android devices are apparently designed for people like me who want the phone to be off when we shut it down. – Matthew Read Jan 15 '11 at 04:37
  • So if it would be able to do it, it should be possible to write a custom alarm clock that can do it? – RoflcoptrException Jan 15 '11 at 07:44
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    @Roflcoptr: No, this is not software problem so you cannot simply write a software. You need hardware alarm clock to be able to turn on an Android phone that is turned off. – Lie Ryan Jan 15 '11 at 13:04
  • I bought the desktop dock. Works well. – ale Jan 18 '11 at 18:19
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Your old mobile phone wasn't really "off" when you turned it off.

Keith Twombley
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    Not necessarily. If the phone had a separate RTC chip you could power off the phone part and have only the RTC powered. When the RTC alarm would trigger it could wake the phone's main micro-controller. I'm surprised Android devices don't feature this kind of hardware. – Miky Dinescu Feb 06 '11 at 22:09
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    Uhh, yes necessarily. If it was running an alarm clock it was on, not off. – Amanda Mar 24 '11 at 00:14
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After setting your alarm, instead of powering off the phone, turn airplane mode on. This way the operating system is closed to an idle state with the clock running.

HTC could link holding the power button to turning airplane mode on and going to standby. An then when the user holds the power button again to turn the phone on, the phone would actually perform a restart. The power on/off function would appear the same as before.

harry
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    I disagree; there are some applications that use a non-trivial amount of power that we would complain about if there were no easy way to save them. This way when we turn off the phone, it uses almost no power at all; the only power used is that by the battery. – Kevin M Nov 16 '11 at 20:47
  • I'm not sure I understand your comment. Do you mean, in Airplane mode there are application running which consume non-trivial amount of power? Or do you mean something else? –  Nov 16 '11 at 21:30
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I did an "experiment" with my phone (Samsung Nexus S, Android 2.3):

Settings --> Date & Time --> Automatic --> OFF

Then I manually set the time to a wrong value (real time + 5 minutes). I switched the phone off. With off I mean really off, not standby, the status when the alarm does not work. After a few minutes I turned it on again.

The time displayed was still the wrong value I set before, i.e. the updated current real time + 5 minutes.

This means that the phone should have an internal clock that works even when it is off. In reality it may not have one, but it should store the delta between the current time obtained from the network and the time I set; however this seems to be quite unrealistic.

So, this makes me think that Android phones have an internal clock with its own battery, and this should be able to make the phone boot at the appropriate time.

Could be something missing in the Android OS itself?

P.S.: Does anyone know if it it possible to make the phone wake up at a specific time? If it was, we just should make it boot five minutes before the alarm is set...

Pietro
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    Interesting idea, but this would only work if no PIN is required, or if you also implement your pin somewhere. or isn't it necessary to enter the PIN to make the AlarmManager working? – RoflcoptrException Apr 03 '11 at 23:52
  • Please don't use your answer to introduce new questions. This is not a discussion forum. If you're not answering the original question, create your own. – ale Apr 04 '11 at 12:46
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    Having an RTC (Real-Time clock) hardware that is running while the phone is powered down does not imply that the RTC can wake up the phone from power off. For the RTC to wake up the phone, it needs to be able to bootstrap the CPU, in essence, having the same machinery as the power button. Also, there needs to be a mechanism for the OS to set the RTC's wake up time, and then it had to store this time inside itself. The mechanism for an alarmed RTC is much more complex than a regular RTC, which is just a simple binary counter. A regular RTC cannot be used to wake up the OS. – Lie Ryan Apr 08 '11 at 12:24
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    However, you've got a point; a CPU is orders of magnitude much more complex than even an alarmed RTC, and addition of alarmed RTC would be very nice, as it allows things that are impossible without one. – Lie Ryan Apr 08 '11 at 12:28
  • Of course it has an internal clock, otherwise you'd have to input the time every time you power off. – Dunhamzzz May 11 '11 at 09:38