In this chapter, we will cover the major components that almost all alarm systems have in common. By the end of the chapter you will realize that the so-called high tech alarm systems and access control systems are not really as complicated as some would like you to believe.
That said, let's get started.
Every alarm system in the world does two and only two basic things.
It monitors the world around it. If the alarm is your neighbor's dog, it keeps an eye on trespassers. If it is an alarm system, then the central control panel monitors a bank of contacts (switches) and waits for something to change (just like the dog). These contacts are the output parts of various kinds of sensors. This is how the sensor tells the panel that something has changed. There are many kinds of sensors, about which I will tell you shortly, but they all signal the panel in much the same way.
When the panel detects a change, it takes an appropriate action based on what the change was. It could be an alarm condition, or it could be a proper access control request. To use the dog scenario again, it could be you coming home from work, in which case the dog wags its tail. It could be the mailman, a bill collector, a burglar, or someone the dog doesn't know. In this case we have an alarm condition and the dog does its thing!
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Cool facts
It doesn't matter if it is the Bank of England or your cottage in Kent, the only major difference is how sophisticated (expensive) the sensors are and how fancy (expensive) the monitoring software is!
Also, I'm sure many of you have seen Tom Cruise drop from the ceiling to avoid the laser grid in Mission Impossible. You could have caught him with a $20 PIR motion sensor and saved yourself the price of the fancy lasers!
In my experience, you don't have to be an electrical engineer to install an alarm system, just a good carpenter, painter, and plasterer! By the way, I'm not, so I'll leave it up to you to hide the wires.
Also, because our alarm system runs on 12 volts, you don't have to be a licensed electrician to install it. If you can plug in a "wall wart" you are there! Fascinated yet? Read on….
And now, more on sensors and how they work.