Why Does My Car Alarm Keep Going Off?


The safety of the vehicle directly depends on the reliability of the car alarm system. if the alarm starts to go off from time to time without the participation of the vehicle owner, you should immediately determine the reasons for the abnormal operation and proceed to their immediate elimination.

Why does the car alarm keep going off on its own?

Among the most possible causes of abnormal activation of car alarms are:

Poor Alarm Installation

Some people prefer to install the car alarm system themselves or someones who is a non-specialist. Even if it is installed correctly, after five to seven years of operation the alarm system starts to “glitch” most often due to broken contacts/connections. In some cases, it is more rational to completely dismantle the old alarm system and install a new one than to constantly contact the car electricians to solve problems with the alarm system.

Dirty/Broken sensor for closing doors, hood, trunk

This malfunction is more common in cars older than 2005. Such cars were equipped with contact sensors (limit switches) that would often deteriorate. The first sign of this malfunction is the unstable arming of the car. First of all, the driver’s door closing sensor usually fails, as it is the most popular one. In this case, closing the doors with the Central lock, they can immediately open.

In modern cars, electronic sensors are used for closing doors and windows, so if the alarm system fails due to them, it is often necessary to replace the entire lock unit. 

Dead battery

If the car’s battery is drained to a critical value, the car alarm may start working in non-standard mode. 2-way alarms with an LCD key-chain usually have an on-Board voltage indication mode. If it is lower than 11.5 Volts, the key-ring will beep. In simpler alarms, sirens may be triggered. In this case, it is necessary to check the voltage on the battery as well as check for power leaks that could lead to the discharge of the battery during parking. Modern car alarms have extremely low consumption currents in the security mode (up to 15 milliamps). If there are no power leaks and a good battery, such car alarms can work for up to six months during a long Parking period without recharging the battery.

Break-in Attempt

Break-in attempts are most often made in the evening and at night. Due to frequent sirens, the owner disables the alarm system to not disturb other people, while criminals use it to break into your car when the alarm is disabled. Criminals cause a false activation of the alarm in the following ways:

  • Throw solid objects into the body
  • Place special devices near the vehicle that contribute to radio interference and vibration of the vehicle.

You can solve the problem in the following ways

  • Enabling silent mode that does not trigger a siren
  • Disconnecting the cable that goes to the siren

Do not completely remove the car from the guard. Most car alarms have a “silent” mode of operation without a siren, which can be programmed from a key FOB. As a last resort, you can go to the car and hardware disable the siren: disconnect one of the conductors that go to it. Residents ‘ peace of mind will be restored, and the alarm system will continue to work. When installing a car alarm system, it is advisable to choose a model that has the function of an immobilizer. In this case, it will be difficult to start the engine in case of unauthorized entry. However, this will not protect the car from theft by evacuation or towing. Usually, hijackers abandon their plans when the emergency light alarm is working, which attracts attention at night.

Broken Key Fob

This happens quite rarely, but this hypothesis should still be tested. It can happen due to a strong impact, getting wet, or unknown external reasons (failure of internal circuit elements). The easiest breakage in this case is the discharge of the battery. This should be avoided, and the battery in the remote control should be changed in time. If you have a key-chain with one-way communication, then to diagnose the battery just press the button and see if the signal light is lit. If this does not happen, the battery needs to be replaced. If you are using a two-way key-chain, you will see a battery charge indicator on its display. If you have a spare keyring – try to use it.

Less common reasons

Usually only occurring in cars older then 2005.

Sensitive sensor

Increased sensitivity of the sensor can lead to false positives in bad weather conditions such as wind or heavy rain. Although In modern car alarms this shouldn’t be an issue since there are usually two-level sensors installed (for weak and strong impacts). Their sensitivity is set during the installation of the car alarm, commonly by adjusting the potentiometers located on the sensor housing. In an emergency, you can temporarily disable the shock/tilt/rolling sensor programmatically or physically by disconnecting the connector from the sensor. A tilt sensor is usually a small unit the size of a matchbox mounted under the steering wheel, with a connector and an LED on the housing. The housing has one or two adjustment holes for the small screwdriver.

Electromagnetic Interference 

Manufacturers usually specify the level of interference immunity in the manual. 

In urban environments, there are areas where the level of electromagnetic field strength far exceeds the maximum possible which can lead to failures. Usually, such zones are close to:

  • Transceivers of base stations of cellular communication
  • Power Lines
  • Trolleybus and tram overpasses
  • Industrial zones


A very common reason for older cars. A typical car alarm installation location is under the dashboard on the left side of the driver’s left knee. Moisture penetrates the installation area along the driver’s side. Most often, the problem occurs in the fall, when rainwater drains under the windshield are clogged with fallen leaves and needles. Plums at this time of year must be periodically cleaned.

If water gets into the alarm unit, then you need to turn off the ignition, remove the battery terminals, and disconnect the car alarm head unit from the connectors. Then you need to carefully disassemble the case, clean the circuit board with a soft brush and medical alcohol (not a solvent!), dry it, you can use a hairdryer at a temperature no higher than 130 degrees Celsius.

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