![]() For very small shifts, where the ball only rolls from one contact to the next one, the brain might not trigger the alarm at all. Based on how many bursts it receives and how long they last, the brain can determine the severity of the shock. When this happens, the brain receives short bursts of current from all of the individual circuits. If the sensor experiences a more severe shock, the ball rolls a greater distance, passing over more of the smaller electrical contacts before it comes to a stop. As it rolls on, it passes over the other contacts, closing each circuit and opening it back up, until it finally comes to a stop. This opens the switch, telling the brain that the ball has moved. As it rolls off of one of the smaller electrical contacts, it breaks the connection between that particular contact and the central contact. When you move the sensor, by hitting it or shaking it, the ball rolls around in the housing. Each of the small contacts is connected to the brain this way, via separate circuits. This completes a circuit, sending an electrical current to the brain. In any possible resting position, the metal ball is touching both the central electrical contact and one of the smaller electrical contacts. ![]() A metal ball that can move freely in the housing.Several smaller electrical contacts at the bottom of the housing.A central electrical contact in a cylinder housing.In the next couple of sections, we'll look at some of the more advanced car alarm systems that protect against craftier criminals. There are other ways to get into the car (breaking a window), and thieves don't actually need to break into your car to steal it from you (they can tow your car away). Turning on a light (by opening the door), messing with electrical wires under the hood or removing an attached trailer with an electrical connection would all cause such a drop in voltage.ĭoor sensors are highly effective, but they offer fairly limited protection. If there is a drop in voltage in this circuit, the brain knows that someone has interfered with the electrical system. When this current flows, it causes the brain to sound the alarm.Īs an overall protective measure, modern alarm systems typically monitor the voltage in the car's entire electrical circuit. With the new wires in place, opening the door (closing the switch) sends an electrical current to the brain in addition to the inside lights. In the following sections, we'll look at a variety of sensors to see how they work and how they are connected to the alarm system's brain.Īll you have to do to set up door sensors is add a new element to this pre-wired circuit. Since cutting the power is a possible indication of an intruder, it triggers the brain to sound the alarm. This hidden battery kicks in when somebody cuts off the main power source (by clipping the battery cables, for example). The brain and alarm features may be wired to the car's main battery, but they usually have a backup power source as well. Security systems differ mainly in which sensors are used and how the various devices are wired into the brain. ![]() The brain's job is to close the switches that activate alarm devices - your horn, headlights or an installed siren - when certain switches that power sensing devices are opened or closed. The brain in most advanced systems is actually a small computer. ![]() A computer control unit that monitors everything and sounds the alarm - the "brain" of the system.An auxiliary battery so that the alarm can operate even if the main battery gets disconnected.A radio receiver to allow wireless control from a key fob.A siren, often able to create a variety of sounds so that you can pick a distinct sound for your car. ![]()
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