How to tell if android device has been turned off

I have an re-occurring alarm manager task that needs to run nightly, However when the device is turned off then back on, it erases this task and I have no way to reset it. I would like to know how to开发者_Go百科 tell if a device has been turned off and/or if you can run specific code before the phone turns off so I can set a flag to reset this task.

Register for the RECEIVE_BOOT_COMPLETED permission and set up a BroadcastReceiver to watch for BOOT_COMPLETED broadcasts.