When looking at home alarm monitoring, it is important to note that all systems are different, working in slightly different ways. Of course, the main goal of any alarm system is the same: As long as it is armed, it detects when someone breaks into the home, alerts the alarm monitoring company, and prompts that company to call the authorities. The police then respond to the call, hoping to get to your house before the intruders have left, thereby protecting your home even when you are not there to watch over it on your own. The ways that the systems detect intruders, though, is how they differ.
The first piece of equipment that almost all systems will have is a sensor on the front door. Similar sensors will be located on the back door and any additional entrances. One piece goes on the frame and the other piece goes on the door itself. If the door swings open for any reason – even if you simply use the key to open it – that sets off the alarm when the pieces move apart from each other. There is usually a slight delay for you to type in the code if it really is you, and then the alarm is triggered.
Similar sensors are often used on windows. If the windows are forced open, or if they are accidentally left unlocked and they are just slid up or out to open them, the sensors will go off. There might be a delay on these, as well, but there often is not. The idea here is that you have to come in through the door to get into your house, which is where the alarm box is, but you are never going to come in through the window. Even if you did, you’d never get to the keypad in time. The system assumes that anyone coming in that way is an intruder.
However, the problem here is that the windows could be broken, meaning that people could get in without moving the sensor. This is where some systems differ, using motion sensors inside the rooms – you just mount them on the wall, with a full view of the room – to detect people walking around in the house. It doesn’t matter how they got in; it just detects them no matter where they are. These work like the sensors for a motion-activated light.