Car care

How does the car anti-theft alarm work? How to turn off the siren

The car anti-theft warning system is a type of security device that helps take measures to protect the car when it detects signs of being broken into by a thief. Car anti-theft systems often protect the car by signaling an alarm with a horn and lights, preventing the car from starting, sending notifications to the car owner… Depending on the structure and installation, each anti-theft system will have Various anti-theft functions.

How does the car anti-theft alarm work? How to turn off the siren
How does the car anti-theft alarm work? How to turn off the siren

Structure of anti-theft system on cars

There are many types of car anti-theft systems. Each type has a different structure and corresponding features. However, most types of anti-theft alarms today have main parts including:

  • Controller (anti-theft ECU): Receives signals from the switch and sensor system, if it detects that the vehicle has been broken into, it will transmit a signal to activate the alarm system.
  • Alarm devices include: Sirens, car horns, headlights and taillights. These devices will help alert surrounding vehicles that are being broken into.
  • The switch system includes: Car door switch, hood switch, luggage compartment door switch, electric lock switch and door lock cluster… These tasks help detect the open/close status, then transmit the signal. to the anti-theft ECU.
  • Sensor system: Intrusion detection sensor helps emit wave signals into the cabin to determine movement in the cabin and send signals to the anti-theft ECU.

See more: What does 4Matic mean? What’s special about this Mercedes system?

Principle of operation of anti-theft system on cars

The anti-theft system on cars has 4 states:

Non-working state: At this time the system is not working, so it will not be detected if a thief breaks in.

Preparing to work state: This is the delay time until the system reaches the alarm state. In this state, the system cannot detect any intrusion.

Working status: When the anti-theft system is active, it can detect if a thief breaks in.

Alarm status: If any door or hood is unlocked unusually strongly, the battery terminal is removed, the glass door is broken, the cabin has unusual movement… the switch and sensor system will transmit a signal. anti-theft ECU signal. After processing, the anti-theft ECU will issue a command to activate the alarm system. At this time, the siren sounded and the car’s lights flashed continuously. In some systems, the ECU also prevents the vehicle from starting.

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What is the Immobilizer anti-theft system?

The Immobilizer anti-theft system is a system that helps prevent the vehicle from starting the engine when the ID code transmitted from the key does not match the pre-registered ID code in the ICM (Immobilizer Control Module). This is a system that helps significantly reduce the rate of car theft in addition to anti-theft warning systems with horns and lights.


Structure of Immobilizer anti-theft system:

Satellite transponder combined with remote signal transmitter: This part is integrated in the vehicle’s ID key set. This is where the vehicle encryption data is stored. If there is no signal from this part, the ECU will disable the vehicle.

Remote control unit for engine start-up prevention system: This part helps receive and transmit signals from the satellite transponder to the ECU.

Components of Security Car Alarm

MICU (with integrated imoes) and ECM/PCM: This unit helps receive and process signals transmitted by the remote control unit of the engine explosion prevention system.

Indicator light: Indicator light helps notify the operating status of the system. If damage occurs, the ECU will send a warning signal to the user through this indicator light.


Operating principle of the Immobilizer anti-theft system

When the ID key is inserted into the ignition and turned to the ON position, the integrated receiver transmits a signal to the satellite transponder. The satellite transponder then broadcasts the encoded signal back to the integrated receiver.


Next, this part will transmit the encrypted signal to the ECM/PCM and MICU. The ECM/PCM and MICU identify this encoded signal. If the signals match, it will provide voltage to control the fuel pump and ignition to start the engine. If the signal is not appropriate, it will prevent the engine from starting.

How to turn off the car’s anti-theft siren

The car anti-theft alarm helps to signal a warning when the car shows signs of being broken into. However, there are also some cases where the siren signals incorrectly and makes a loud noise, affecting everyone around. Here are some ways to turn off the car’s anti-theft horn in these cases.

Alarm Siren Resized

Open the driver’s door

In case the anti-theft siren sounds loudly but the remote control does not work, you should use the key to open the driver’s door. Normally after the door opens the buzzer will turn off. If the door is open, try locking it and opening it again with the key.

alarm system

Start the car

Starting the car is a quick way to turn off the car’s anti-theft siren. Most anti-theft alarm systems will automatically turn off and restart when the vehicle starts.

Remove the battery terminal

The siren operates based on the vehicle’s electrical system. Therefore, if you remove the car battery terminal , the anti-theft alarm will turn off. Use a wrench to remove the negative post of the battery. After the buzzer turns off, reinstall the pole.

Remove the system fuse

Look in the car’s fuse panel and remove the fuse of the siren, the siren will turn off.


Take the car to the garage

In case you have tried all of the above methods and still cannot solve the problem, you should take the car to the garage for inspection and repair.

See more at: Car care vip

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