Alarms and Shabbat

Question

Those who have alarms know that even when the alarm is off, when you open a door usually a light goes on or it blinks. There are new alarms in which you can turn all these lights off. However, even though you don't see the lights, obviously something is going on inside the alarm. I.e., you have caused some circuit to do something when you open the door, even though this is not reflected with any lights on the alarm pad. I assume there is nothing wrong with this, although I just want to confirm it. If this would be a problem, than it would be impossible for a Sabbath observer to have an alarm system in his house.