This Post ll help you to manage your alarm :

AlarmManager am=(AlarmManager)getSystemService(ALARM_SERVICE);

Intent alarmintent1=new Intent(MainActivity.this, AlarmReceiver.class);
PendingIntent sender1=PendingIntent.getBroadcast(SpeedMotors.this, 100, alarmintent1, PendingIntent.FLAG_UPDATE_CURRENT | Intent.FILL_IN_DATA);

try {
    am.cancel(sender1);
} catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    System.out.println("ex....."+e);
}

Calendar cal=Calendar.getInstance();
cal.add(Calendar.SECOND, 5);


am.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), 1000*10, sender1);
System.out.println("alarm set...........");

We can also set one time alarm by using set(int type, long triggerAtMillis, PendingIntent operation) method.