Develop Reference

What will alarm manager do if I change phone's time?

I set multiple alarms and in order to control them I change my phone's time. They will work normally ? What In other words, will alarms collapse if I change my phone's time?

Well it all depends on the type you have passed in the set method of alarm Manger.
if you have used ELAPSED_REALTIME or ELAPSED_REALTIME_WAKEUP, alarm will not trigger
ELAPSED_REALTIME
Added in API level 1
int ELAPSED_REALTIME
Alarm time in SystemClock.elapsedRealtime() (time since boot, including sleep). This alarm does not wake the device up; if it goes off while the device is asleep, it will not be delivered until the next time the device wakes up.
if you have user RTC or RTC_WAKEUP, alarm will be triggered according the device time
RTC
Added in API level 1
int RTC
Alarm time in System.currentTimeMillis() (wall clock time in UTC). This alarm does not wake the device up; if it goes off while the device is asleep, it will not be delivered until the next time the device wakes up.

I don't know what you mean by collapse. But the alarm is only aware of the device's time and so if you do change your device time, it should work against that instead.

Turn off AlarmManager when phone goes to sleep mode

I have AlarmManager set up to fire every minute. However, I only need it when phone is active. I want to turn off all updates when phone goes to sleep. I am not sure what the default behavior of AlarmManager and widgets in general is when phone goes to sleep. But I noticed that my battery goes down when in sleep mode. Hence, i believe its the widget thats bringing it down.
So, if AlarmManager and other broadcasts keep firing by default, how can I turn these updates off in sleep mode and then turn them back on when phone resumes active mode?

Use public void setInexactRepeating (int type, long triggerAtMillis, long intervalMillis, PendingIntent operation) with RTC as type. Only RTC_WAKEUP and ELAPSED_REALTIME_WAKEUP will wake up devices.
E.g. in my code I use
am.setInexactRepeating(AlarmManager.RTC, System.currentTimeMillis() + syncInterval, syncInterval, pendingIntent);

About the difference between the alarms of type of AlarmManager.RTC_WAKEUP and AlarmManager.RTC

What is the difference between the alarms of type of RTC_WAKEUP and RTC?
From the documenatation of the AlarmManager, it seems that alarms of RTC will not wake up the device if the device current is asleep, and will not delivered until the next time the device wakes up.
But I found that the alarm of type of RTC will still wake up the device, so what's going on?
What I did is to change the type of RTC_WAKEUP to RTC in the AlamrManagerService.java, function setRepeating(), and then set an alarm of 3 minutes from now on, then check the device, you will find that it still could be waken up by the alarm.

THere are other instances reporting AlarmManager.RTC seems to wake up the device:
AlarmManager.RTC doing too many updates on wakeup
Android AlarmManager RTC doesn't pause while device is sleeping
Allowing the phone to sleep while using RTC alarm on Android
Each time, the root cause is the same:
Something keeps the device awake (even though the screen is black).
Don't forget that a charging device (connected to power) isn't sleeping.

Android: pause Widget updates using Alarmmanager

I just went through this tutorial:
update-widget-in-onreceive-method
(btw: would you propose any improvements to that code?)
At the end someone mentions:
I'm just wondering if there is a way to extend this further so that when the device is asleep (screen off), the updates stop. Then when the device wakes up, the updates resume.
So my question: is there a way of doing this? how?
or is the alarmmanager automatically stopped? - I don't think so.

You can specify whether the device will wake up when scheduling the AlarmManager.
Quote from the documentation:
ELAPSED_REALTIME
Alarm time in SystemClock.elapsedRealtime() (time
since boot, including sleep). This alarm does not wake the device up; if it goes off while the device is asleep, it will not be delivered until the next time the device wakes up.
ELAPSED_REALTIME_WAKEUP
Alarm time in
SystemClock.elapsedRealtime() (time since boot, including sleep),
which will wake up the device when it goes off.
Same goes for AlarmManager.RTC and AlarmManager.RTC_WAKEUP
So you probably want one of the two AlarmManager.RTC or AlarmManager.ELAPSED_REALTIME. These continue while the device is awake and stop when the device is in standby. If this alarm is triggered while the device is asleep it will be delivered when the user turns the device back on though, exactly what you want. And no, the AlarmManagers scheduled alarms are not cancelled automatically in general.
The part mentioned here can be found in this part of the tutorial, specific this line:
alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), 20*1000, pendingIntent);

Android Alarm What is the difference between four types of Alarm that AlarmManager provides and when to use what?

I want to know the difference between RTC, RTC_WAKEUP, ELAPSED_REALTIME, ELAPSED_REALTIME_WAKEUP.
I want to write an alarm application where I will set alarm and close my application and expect for alarm for the time set.
There will be multiple alarms. Right now I am writing for emulator but later will test on device. In emulator, once I set the alarm and close the emulator and restart it, then will it be cleared, as I find with RTC, RTC_WAKEUP and ELAPSED_REALTIME. I am confused. Should I used ELAPSED_REALTIME_WAKEUP? I have not seen any tutorial using ELAPSED_REALTIME_WAKEUP.
please explain.
Thanks.

ELAPSED_REALTIME
Alarm time in SystemClock.elapsedRealtime() (time since boot, including sleep). This alarm does not wake the device up; if it goes off while the device is asleep, it will not be delivered until the next time the device wakes up.
ELAPSED_REALTIME_WAKEUP
Alarm time in SystemClock.elapsedRealtime() (time since boot, including sleep), which will wake up the device when it goes off.
RTC
Alarm time in System.currentTimeMillis() (wall clock time in UTC). This alarm does not wake the device up; if it goes off while the device is asleep, it will not be delivered until the next time the device wakes up.
RTC_WAKEUP
Alarm time in System.currentTimeMillis() (wall clock time in UTC), which will wake up the device when it goes off.

Types of Alarms :
ELAPSED_REALTIME – Fires the pending intent after the specified length of time since device boot. If the device is asleep, it fires when the device is next awake.
ELAPSED_REALTIME_WAKEUP – Fires the pending intent after the specified length of time since device boot. It wakes up the device if it is asleep.
RTC – Fires the pending intent at a specified time. If the device is asleep, it will not be delivered until the next time the device wakes up.
RTC_WAKEUP – Fires the pending intent at a specified time, waking up the device if asleep.

There are two general clock types for alarms: "elapsed real time" and "real time clock" (RTC). Elapsed real time uses the "time since system boot" as a reference, and real time clock uses UTC (wall clock) time. This means that elapsed real time is suited to setting an alarm based on the passage of time (for example, an alarm that fires every 30 seconds) since it isn't affected by time zone/locale. The real time clock type is better suited for alarms that are dependent on current locale.
Source: https://developer.android.com/training/scheduling/alarms.html

From the site you can get the difference between the 4 constanst
Below is example of the setting alarm
Calendar mCalendar = Calendar.getInstance();
mCalendar.add(Calendar.SECOND, 20);
Intent intent_Timer = new Intent(TimerEvents.this, AlarmReceiver.class);
intent_Timer.putExtra("alarm_message", "Drax Rules!!!");
// In reality, you would want to have a static variable for the request
// code instead of 192837
PendingIntent sender = PendingIntent.getBroadcast(this, 192837,
intent_Timer, PendingIntent.FLAG_UPDATE_CURRENT);
// Get the AlarmManager service
AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);
am.set(AlarmManager.RTC_WAKEUP, mCalendar.getTimeInMillis(), sender);
Hope this will be helpful to you