AlarmManager

AlarmManager schedules time-based operations. You tell Android:

“At this time (or every X minutes), wake up and do this.”

Typical uses

1. Run work at a specific time

Examples:
- Show a notification at 9 AM
- Trigger a daily reminder
- Schedule an event in the future
This works even if:
- Your app is killed
- The user hasn’t opened it in days
- The device was idle

2. Periodic tasks (with caveats)

Sync data every few hours
Refresh something daily

But Android now aggressively batches and delays alarms to save battery. Precision is optional unless you explicitly demand it.

3. Wake the device

AlarmManager can wake the device from sleep using wake-up alarms.

How it works internally

AlarmManager does not run code directly.
It triggers a PendingIntent.
That PendingIntent usually starts:
- A BroadcastReceiver
- A Service
- An Activity (rare and annoying)

So AlarmManager is basically a time-based Intent launcher.

Alarm Types

1. Inexact alarms (recommended)

setInexactRepeating()
System groups alarms together to save battery

Use when exact timing does not matter.

2. Exact alarms

setExact()
setExactAndAllowWhileIdle()

Use only when:

Timing must be precise
You accept battery drain
On Android 12+, you may need EXACT_ALARM permission

3. Repeating alarms

Mostly discouraged now.

The system prefers rescheduling alarms manually after each trigger.

What AlarmManager is NOT good for

Long-running background work

Frequent background tasks

Network-heavy jobs

Modern alternatives

Because developers abused AlarmManager into battery extinction.

WorkManager: Best for deferrable background work. Respects system rules.
JobScheduler: Lower-level, system-managed background jobs.

Rule of thumb:

Exact time needed? AlarmManager
Eventually is fine? WorkManager

Example

Show the time picker dialog:

Calendar calendar = Calendar.getInstance();
int hour = calendar.get(Calendar.HOUR_OF_DAY);
int minute = calendar.get(Calendar.MINUTE);

TimePickerDialog timePickerDialog = new TimePickerDialog(MainActivity.this, new TimePickerDialog.OnTimeSetListener() {
    @Override
    public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
        Calendar c = Calendar.getInstance();
        c.set(Calendar.HOUR_OF_DAY, hourOfDay);
        c.set(Calendar.MINUTE, minute);
        c.set(Calendar.MILLISECOND, 0);
        Log.d(TAG, "onTimeSet: ");
        setAlarm(c);
    }
}, hour, minute, false);

timePickerDialog.show();

Set the alarm:

Intent intent = new Intent(this, AlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 1, intent, PendingIntent.FLAG_MUTABLE);

AlarmManager alarmManager = getSystemService(AlarmManager.class);
alarmManager.setExact(AlarmManager.RTC_WAKEUP, c.getTimeInMillis(), pendingIntent);

Last modified: 05 February 2026