How an alarm works
Let’s have a look at how an alarm system works. Sometimes I am truly amazed at how basic it can be. I think you will be too. You won’t need to be an electronics whiz. Just sit back, relax, and be amazed.
First, both commercial and residential alarm systems for the most part work very much alike . The operating theories are identical. In fact, many alarm companies use the same equipment for both.
The system basically consists of an alarm master control box that works on very low voltage, usually about 6 to 12 volts. The inside of the box looks complex, but it’s really very simple. The wires come out of the control box, go around the interior of the building, and then back into the control box. This is commonly referred to as the protection loop or alarm circuit.
Simple so far, right? Wrong. It gets a little more complicated now. To make the master control box activate an alarm, detection devices are connected to that protection loop that goes around the inside of the building. These devices are wired in such a way that when they are triggered, the alarm master control box will sense this and activate the alarm system. Usually a loud bell or siren will be attached to the control as well as some type of central-station monitoring. (We’ll look at individual devices and how they work in Chapter 2).
To make things simple, think of the alarm master control box as a water source such as an ocean and the wires that loop around the inside of the building as a long, continuous river. The water flows out of the ocean and into the river, which does what? Right, flows around and back into the ocean again. An alarm basically works the same way. As an example, see Figure 1.
The alarm control box activates when the flow of low-voltage current that runs through the wiring around the building is interrupted by one or more of the detection devices. To make this clear, let’s look at another example. Imagine that the wiring that loops around the inside of a particular building is a water pipe. If we place a shut off valve on the pipe and close the valve, the water won’t be able to complete the loop. Simple, right? Right. But rather than water current running through a pipe, electric current runs through the wiring, which goes around the perimeter of the building. Detection devices are connected individually to the loop in various configurations, each having the ability to interrupt the power flow back to the control. A steady flow of current going out of the control and returning will not activate the alarm. However, if the wiring is cut or one of the detection devices connected to that wiring loop is activated, it is just like turning off a shut-off valve. The alarm master control box senses a loss of power in the wiring loop, and this trips a relay, which activates an alarm.
To review briefly, the low voltage goes out of the master control box and runs through the wires around the interior of the building and back to the control box. Detection devices are connected to that wiring loop. If they sense any problem, they act as a shut-off valve, which prevents the low voltage from going back to the control box. What happens? Since the control box senses a break in the flow, it activates and creates lots of bells and whistles. If the system is monitored, a signal will be sent to the alarm company monitoring station.
It is so simple that if your having a problem following the theory, you may be wanting to believe it’s more difficult than it really is. This chapter is important because the other chapters are built on it. If you feel somewhat lost at this point, please review it again. As you read, the light bulb in your head will turn on as to how simple this all really is.
A word about safety. I recommend that you not attempt any of the following circumvention techniques unless you have been professionally trained in the area of electricity. If you touch the wrong wires, you can be injured. Please keep in mind that the only intention of this book is to explain how alarm systems work so you can develop a more secure system for yourself.