builder.setPriority(Notification.PRIORITY_MAX).setCategory(Notification.CATEGORY_ALARM)
                .setContentTitle(getString(R.string.alarm_title))
                .setContentText(getString(R.string.alarm_text))
                .setSmallIcon(R.drawable.ic_alarm_black_24dp)
                .setSound(alarm_sound, attributes);
Notification notif = builder.build();

notif.flags |= Notification.FLAG_ONGOING_EVENT | Notification.FLAG_INSISTENT;