how car alarms work - car alarm with remote start
In the last section, we studied the door sensor, which is one of the most basic car alarm systems.
Today, only the cheapest car alarms rely on door sensors.
Advanced alarm systems rely mainly on vibration sensors to stop thieves and vandals.
The concept of impact sensors is fairly simple: if someone hits, pushes, or otherwise moves your car, the sensor sends a signal to the brain indicating the intensity of movement.
Depending on the severity of the electric shock, the brain issues a warning horn beep or a complete soundscale alarm.
There are many different ways to construct impact sensors.
A simple sensor is a long and flexible metal contact located above another metal contact.
You can easily configure these contacts as simple switches: The current flows between them when you touch them together.
Large bumps can cause flexible contacts to swing, thus touching the contacts below and completing the circuit briefly.
The problem with this design is that all shocks or vibrations close the circuit in the same way.
The brain is unable to measure the intensity of the vibration, which leads to a lot of false alarms. More-
Advanced sensors send different information according to the severity of the impact.
The design shown below was patented by Randall Woods in 2000 and is a good example of this sensor.
The sensor has only three main elements: the metal ball is exposed to the central electric contact and a smaller electric contact at any possible stationary position.
This completes a circuit that sends a current to the brain.
Each small contact is connected to the brain in this way through a separate circuit.
When you move the sensor, the ball rolls in the shell by tapping or shaking the sensor.
When it rolls down from a smaller electrical contact, it disconnects the connection between that particular contact and the center contact.
This turns on the switch and tells the brain that the ball has moved.
As it rolls, it closes each circuit and re-opens it through other contacts until it finally stops.
If the sensor is hit more seriously, the ball rolls a larger distance and passes through more smaller electrical contacts before stopping.
When this happens, the brain receives a short current from all individual circuits.
The brain can determine the severity of the electric shock based on the number and duration of emergencies it receives.
For very small moves, the ball rolls only from one contact to the next, and the brain may not trigger an alarm at all.
A slightly larger shift-
For example, someone hit the car. -
It may send a warning signal: tap the horn and flash the headlights.
When the ball rolls far away, the brain turns on the siren completely.
Vibration sensors are the main anti-theft detectors in many modern alarm systems, but they are usually combined with other devices.
In the next few sections, we'll look at some other types of sensors that tell the brain when something goes wrong.