AlarmManager am = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);

int ALARM_TYPE = AlarmManager.RTC_WAKEUP;

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)

    am.setExactAndAllowWhileIdle(ALARM_TYPE, calendar.getTimeInMillis(), pendingIntent);

else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)

    am.setExact(ALARM_TYPE, calendar.getTimeInMillis(), pendingIntent);

else

    am.set(ALARM_TYPE, calendar.getTimeInMillis(), pendingIntent);