What to do if a car alarm goes off on its own

Self-activated car alarm: the causes and the correct actions of the car owner

Car alarm system is put for the safety of the vehicle. It should always stand guard. But after all, the alarm system itself may fail and work incorrectly. This situation must be corrected as soon as possible, because the attackers can take advantage of such a state of affairs and promptly steal the car.

Independent activation of the alarm system on the car

More often than not, the alarm system works by itself. Many motorists are faced with such a problem, but few of them know what to do. We decided to correct this situation.

Causes of abnormal alarm responses

There are a large number of reasons why the alarm system turns on by itself in the car. This circumstance significantly complicates the diagnosis, identification of the true cause and its further elimination. Below we have listed the most common circumstances that can cause such a problem:

  • malfunctions in the sensitivity adjustment of the sensors, which track impact, tilt and roll;
  • rattling contacts of the sensors that control the process of closing the trunk, doors and hood;
  • low or full discharge of the battery and the presence of leaks in the power circuits;
  • the area where the car is parked is in the area of electromagnetic interference, which at high levels can disrupt alarm operation;
  • problems with electrical wiring;
  • unstable operation of the CAN bus;
  • moisture on the main unit of the alarm system;
  • problems with the volume sensor;
  • intruders can also cause abnormal responses of the system.

Everyone can have any of these situations in their lives. We just have to look at each of these causes and give tips on eliminating them that will be useful in practice.

What to do in these cases?

As you can see, there are many causes. Each of them affects different working nodes. The elimination of each of these causes is carried out differently. Therefore, there is nothing left for us to do but to consider each of the possible options.

Deliberate actions of car thieves

This reason for triggering the security system is a classic, the most common case. The burglars usually use the standard scheme. They act at night when you can catch the car owner off guard and his reaction to what is happening is not quite adequate. The car alarm goes off as if by itself several times. Usually after three actuations the owner concludes that the system is faulty. The anti-theft alarm goes off, and the owner continues to dream, deciding to take care of the repairs in the morning.

The problem does disappear in the morning, though, along with the car. You need to be vigilant if you want to keep your property intact. To activate the security system, the intruders use different methods, their professionalism and ingenuity is growing by leaps and bounds.

Car thief next to the car

In such cases, you should act as follows:

  • Under no circumstances should the alarm system be disarmed;
  • you can use the silent mode, which is found in many modern systems;
  • go down to the car and investigate the situation, if necessary call the police.

Incorrect adjustment of the shock sensor sensitivity

This mechanism is sensitive, even very sensitive. Therefore, triggering of the alarm can be observed in bad weather. Many modern systems are equipped with two-level sensors, such as Tomahawk alarm systems, which very rarely act on their own. The sensitivity of such systems is regulated at the stage of installation of security systems. With high sensitivity false activation is possible.

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In case of an emergency, the sensor can be disabled programmatically or technically. The sensor is usually located under the steering wheel, presented in the form of a small unit. It is equipped with a connector and an LED. The design is equipped with adjustment holes, which require the use of a small screwdriver “on the plus”. The process of adjusting the sensitivity level is carried out according to the instructions that come with the security system.

It is not only improper adjustment of the sensor that can cause incorrect operation. The sensor can be fixed incorrectly. Plastic clamps are usually used for its installation. Over time, they deteriorate, and the sensor hangs loose without any fixation. In this state it can be triggered even by a light breeze. The solution to the problem is simple – replace the fixing clamps.

Bouncing of contacts of sensors of closing doors, hood and trunk

This problem is most often encountered by owners of cars manufactured before 2005. In such cars, there are contact sensors or limiters, which quickly become unusable. You can determine such a malfunction by the inconsistent setting of the vehicle on the alarm. Initially, the sensor on the driver’s door fails, since it is used most often.

The problem is solved by adjusting the curtains and brackets on the door locks, which are located on the rack. In most cases, this solves the problem. Another solution is to replace the limit switches.

As for more modern machines, there are already installed electronic mechanisms. If the alarm system does not work properly due to their cause, you have to perform a complete replacement of the locking units.

Battery discharge

The work of the car alarm system directly depends on the battery, or rather on its charge. Discharging the battery to a critical level leads to malfunctions of the car alarm system.

If the system is bi-directional, then most likely its design includes a mode that indicates the voltage in the on-board network. When the voltage drops below 11.5 volts, the key fob alerts its owner by means of an audible alert. In the case of simple systems, the siren may activate when the voltage is low.

The car owner should check the battery voltage, diagnose the power supply circuit, which may have leaks. Now there are alarm systems with very low power consumption. An example of such a system is the car alarm Panther, which itself is triggered very rarely. Such devices can work up to six months, but this requires a good battery and a good power circuit.

Car alarm Panther

Electromagnetic interference in a parking lot

In the data sheet, which is necessarily attached by the manufacturer to the security system, the permissible level of electromagnetic interference and interference immunity index is specified. In many populated areas, especially in large cities, there are places with high electromagnetic field strength. In such conditions, malfunctions of car alarms can occur.

Such places are often near the following objects:

  • cellular receiving and transmitting points;
  • power lines;
  • overpasses on which public transport (trolleybuses, streetcars) move.

There will be only one solution to the problem here – look for another parking lot. There are no other options.

Bad contacts

A problem of this nature occurs in the case of improper installation of the security system, which was carried out by craftsmen without specialization and experience. Electrical installation rules are violated and the car owner has to deal with incorrect operation of the security system. But even with proper installation problems may arise after 5-7 years of active operation. During this time the contacts and connections deteriorate and need to be replaced. Even a reliable Sherkhan alarm system can go off on its own because of problematic contacts.

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There may be two options here:

  • appeal to auto electricians, who will diagnose the system and replace the faulty connections and contacts;
  • Installing a new system.

The latter option often turns out to be more rational, that’s why more car owners choose it.

Car CAN bus malfunctions

CAN-bus is a local car network, which connects all the control units of the car into one system. Previously, security systems received information from a sensor from each door. Now the systems collect information about the car via CAN-bus. The information is complete and extensive, covering all data that pertains to the vehicle.

CAN-bus of the car

In most cases the CAN bus is represented as a twisted pair with different levels. If the integrity is compromised, the signal is lost and does not reach the alarm system. It perceives this state of affairs as the actions of intruders.

It is very difficult to return the CAN-bus to its former functionality. Without the services of a specialist there is no way around it. You must have patience and be prepared for serious financial expenses.

Moisture on the main unit of the alarm system

Owners of older cars encounter such malfunctions. For the installation of the alarm system often chooses a place under the dashboard in the area of the left rack. Moisture penetrates along the post, located on the driver’s side of the seat. This problem occurs more often in autumn than in the rest of the year, because fallen leaves form clogs in the structural drains.

So what to do if the alarm turns on by itself exactly because of moisture? The first thing to do is to clean the drains. This will avoid the problem. If there is already water in the unit, you need to act as follows:

  • turn off the car;
  • remove the battery terminals;
  • disconnect the alarm unit from the connectors;
  • disassemble the housing, proceed carefully;
  • Clean the board, using a brush with a soft lint and medical alcohol, in any case do not use a solvent;
  • leave the board to dry;
  • assemble the unit, connect it and check the operation of the system.

Faulty or incorrectly installed volume sensor

This mechanism is not mounted on every car and is not found in every security system. You need to know how to install it correctly. If mistakes were made during installation, the alarm will beep at every passerby. In such cases, the sensor should be disabled and already in a quiet situation, away from crowded places, to experiment with its location.

Alarm system, properly installed, is the guarantee of your peace of mind and the safety of your car. You should not ignore the false activation of the alarm. You need to deal with the arisen problem, conduct diagnostics and eliminate the cause of incorrect operation. Do not accumulate problems, in the future it will only be even more difficult to eliminate them. And they will not disappear by themselves either.

Why does the car alarm constantly actuates by itself after a certain period of time for no reason?

Disabling the alarm system in the car

There are many reasons why the alarm goes off by itself. The siren yells because of improper installation or high sensitivity of the sensors. First, you need to make sure that the system is set up normally. After that, diagnose the electrical circuits of the anti-theft system.

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Why the alarm system activates and what to do

Unintentional activation of the alarm mode in security systems of common manufacturers contribute to the following reasons:

  • malfunctions in the operation of shock and tilt sensors;
  • ingress of moisture in exterior parts of the system;
  • overloading of the machine;
  • short circuit of security system limit switches (alarm system activates by itself when contacts oxidize).

Improper adjustment of sensor sensitivity

The set of any anti-theft system includes sensors that respond to shocks and changes in the position of the body. The principle of the part is to detect vibration and send a signal to the siren, which activates and does not turn off. Sensors of any alarm system must be properly configured. The procedure for performing the work includes the following steps:

  • Determining the location of the sensors. In older models of security systems, the sensors are located near the head unit, to which they are connected via cables. The housings are equipped with bolts, by means of which the sensitivity is adjusted. In modern models of anti-theft systems, the sensors are built into the head unit.
  • Adjustment. Using a screwdriver with a shaped nozzle tighten the existing bolts on the bodies. It is necessary to be able to change the parameters correctly, otherwise the alarm system on the car for no reason will be triggered often. You should not set a high degree of sensitivity, since the sensors will react to the slightest vibration.

Alarm system shock sensor

Parameters of the sensors of a modern alarm system are adjusted with a key fob. Adjustment of the sensors is performed as follows:

  • The system is disarmed. The control unit is prepared for programming.
  • Press 1 and 2 buttons on the key fob. Location of service keys and their names depend on the brand and model of anti-theft complex.
  • Sensitivity of the sensor is adjusted with the buttons. Each level means the degree of sensor reaction. It is necessary to choose average values, at which false triggering of the car alarm will not be observed.

Bad contacts

Damage to electrical circuits, insulation failure and disconnected contacts can cause the alarm system to turn on by itself at night, giving the owner anxiety. Such malfunctions occur if the anti-theft system is installed incorrectly. The probability of damage to electrical circuits is higher in devices that can block the engine, fuel tank or ignition switch. Such a malfunction cannot be eliminated without the help of specialists. In this case, contact a car service.

Battery discharge

If the battery charge is minimal, the alarm is activated all the time. Two-channel security complexes with an LCD display notify about the lack of power sound and symbolic indication. Triggering of a simple system is to activate the siren. You can eliminate the malfunction by performing the following actions:

  • With the engine off, determine the battery voltage with a voltmeter. If the instrument displays a number less than 11.8, the battery should be charged. A value in the range of 12.5-13 V is considered normal.
  • Check for damage in the electrical circuits. The latter lead to a rapid discharge of the battery. Check the system with a multimeter, switched to ammeter mode. The minus contact is connected to the ground terminal, the plus contact is connected to the battery. With the electronic devices disconnected, the multimeter probes the break points. If there is a leak, connect the elements of the system one by one. Normalization of the current helps to understand which part of the circuit is damaged.
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Checking voltage with a voltmeter

Improper operation of volume sensors

If the sensor is installed in the wrong place, the sensor may be triggered by movements occurring near the car. Removing the system element and changing its location helps to solve the problem. The alarm may go off when the car is overloaded. The sensor will trigger a change in the amount of air, mistaking it for an attempt to steal the vehicle.

Excessive moisture

Moisture on the electrical wiring causes the alarm to activate for no reason. The following causes contribute to increased humidity:

  • Heavy rains;
  • condensation caused by sudden temperature changes (in this case the siren is triggered at night);
  • clogging of gutters designed to carry away rain water;
  • Liquid penetration into the head unit and sensors during machine washing.

Car Wash

To eliminate the problem, you need to perform the following actions:

  • turn off the engine;
  • disconnect the battery terminals;
  • disconnect the cables supplying the alarm head unit;
  • after de-energizing the onboard network, remove the sensor housings and the control unit;
  • soak the electronic board with a soft cloth or brush;
  • dry all parts of the system using a hair dryer with warm air.
  • install the part housings, connect the cables;
  • arm the alarm system.

Oxidation of limit switches

The problem often occurs when installing the alarm system on older cars. The limit switches in this case are placed on the hood, door and trunk. These parts quickly fail and begin to operate even without trying to open the lock. To eliminate the malfunction, the following work should be carried out:

  • restore the correct position of the parts of the locks (the hinges are adjusted with an Allen key);
  • clean the oxidized areas with sandpaper;
  • Replace severely damaged limit switches.

Replacing the alarm limit switch under the hood

Modern cars are equipped with electronic locking sensors. If the alarm does not turn off due to their malfunction, the locking units are replaced completely.

Electromagnetic interference at the parking place

In metropolitan areas, there is an increased intensity of the electromagnetic field, leading to interruptions in the operation of security systems. Spontaneous activation of the alarm mode is observed at a pronounced excess of the norm specified in the technical passport of the car alarm system. Triggering of the siren occurs near mobile operators’ towers, power lines, streetcar and trolleybus tracks, industrial areas. The only way to solve the problem is to change the parking place.

CAN bus malfunction

This on-board network element is a pair of cables of different levels. If the bus is damaged, the information transmitted by the sensors is lost. The alarm system recognizes such a malfunction as an attempt to steal the vehicle, which results in false alarms. Troubleshooting CAN-bus requires special skills and special equipment. Such work is performed in the service centers.

CAN-bus of the car

Methods of malefactors

Criminal actions are most often committed in the evening and at night. Due to the frequent triggering of the siren, the owner disables the alarm system so as not to disturb the occupants of the house. False triggering of the alarm is caused by criminals in the following ways:

  • Throwing hard objects into the bodywork;
  • placing special means near the car, contributing to radio interference and vibration of the car.

Breaking into the car

Specialists recommend not disarming the alarm system in case of criminal actions. The problem can be solved in the following ways:

  • turning on the silent mode, not accompanied by triggering the siren;
  • disconnecting the cable going to the siren.
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To protect the vehicle from theft helps to choose security systems, equipped with an engine blocker and light indication of the alarm mode.

Features of problems with alarm systems of different manufacturers

Causes of false alarms in anti-theft systems from different manufacturers can vary.

Starline A91

Starline car alarm system becomes often triggered due to improper installation or weakness in the attachment of parts. The principle of operation of the sensors is based on the advance occurrence of a sound pulse. To spontaneously did not trigger the A 91, you need to adjust the sensitivity of the sensors. To do this, proceed as follows:

  • reduce the values of both areas by adding a few points for the warning zone;
  • the alarm system is switched to alarm mode;
  • after a minute touch the body, which helps determine the degree of sensitivity of the sensor;
  • if necessary, the values are reduced again;
  • The same actions are performed for the alarm zones of sensors Starline auto alarm system.

The recommended sensitivity of the sensors – 14, the lowest – 0.1. When you set the value to zero sensors will not work.

Tomahawk 9030

Tomahawk car alarm system can turn on spontaneously due to the following reasons:

  • Installation of sensors on plastic parts. When this material cools, it creates vibration, to which the anti-theft system reacts. Installation of sensors on the metal part of the body helps to eliminate the problem.
  • Incorrect setting of the timer. In this case, the siren begins to turn on at certain intervals. Resetting the settings helps to solve the problem.


Sheriff security complex often turns on, especially in such situations:

  • Rain on the hood (when the system is installed under the steering column). In this case, it is recommended to move the sensors to the middle part of the body.
  • The headlamp is set to activate when the doors are opened. If this part of the system is equipped with a diode, the anti-theft device will stop responding to the interior lighting.


A frequent cause of spontaneous activation of the alarm mode is the increased sensitivity of the sensors. If after adjusting the indicator the problem is not solved, you need to move the sensors and assess the state of the limit switches.


The cause of malfunctions in this anti-theft system is the breakdown of the limit switches. Contacts of these parts get oxidized, so you should assess their condition and clean them. If the security complex Pantera responds to passing vehicles, you need to change the sensitivity of sensors. After that, the car is put on the handbrake, de-energize the onboard network and perform diagnosis of electrical circuits, checking the places of connections.

Sherkhan 5

In case of Sherkhan Magikar false triggering you should do the following:

  • disable additional functions;
  • clean the contacts of the door limit switches (if necessary the parts are replaced);
  • Check the installation of the system (false alarms occur if the sensors are only equipped with the car doors).


If the alarm mode is triggered frequently, you need to assess the operating conditions of the security complex. Spontaneous triggers occur in frosty weather. The malfunction can occur when the key fob is placed near the steering column or improper connection of the system.

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