The car alarm buzzing for no reason is a common issue reported by many people.
The problem gets even more frustrating at night when people are sleeping, and suddenly your car alarm goes off with no apparent reason.
Why does this happen? Luckily the alarm is not getting off every time because of a thief; sometimes, a faulty installation or other reasons also cause the alarm to go off.
7 Causes Why Your Car Alarm Keeps Going Off
- Low Battery Charge
- Sensitive Shock / Movement Sensor
- Faulty Hood Latch Sensor
- Faulty Door Lock Sensor
- Faulty Key Fob
- Incorrect Alarm Installation
- Bad Alarm Control Module
Here is a more detailed list of the 7 most common reasons your car alarm keeps going off.
Low Battery Charge
A bad car battery or low battery charge is a widespread problem for a car alarm that goes off during the night. If you hear the car alarm going off at night and the car battery is dead in the morning, the car battery may be bad.
If your car battery is going off, but you can still start your car with no problems, it is most likely something else faulty, though.
You can test your car battery with a car battery tester, to see how good it is and replace it if it is bad.
Sensitive Shock/Movement Sensor
A sensitive shock or movement sensor triggers the alarm even if a dog or a cat gently touches your car. The type of shock sensors and movement sensors you have in your car depends a lot on your car model and if the car alarm is an aftermarket alarm system installed in your car or a car alarm from the factory.
In some car models with a car alarm from the factory, you can program the shock and movement sensors’ sensitiveness with a diagnostic scanner.
This is often needed on cars like Audi and Volkswagen because their sensors are over-sensitive from the factory and will go off sometimes.
Some aftermarket car alarm systems do also have adjustable sensors. Check the car alarm manual for more information.
Faulty Hood Latch Sensor
Modern vehicles have a hood latch sensor, which triggers the alarm if someone is trying to force open your car’s hood.
Depending on your car’s condition, very likely dust, grime, and debris will collect where the hood latch sensor is located, and this causes the alarm to go off.
To fix this problem, locate the sensor and have it cleaned. If you can still hear the alarm sound, maybe someone tried to tamper with the sensor or the sensor is damaged. Replace the sensor if you think it may be faulty.
You can find the hood latch sensor inside the hood lock most of the time, but it can also be installed externally.
Faulty Door Lock Sensor
The same as with the hood latch sensor, your car alarm monitors your car doors to make sure no one is opening your door.
Therefore a faulty door latch sensor can cause the car alarm to go off. The door latch sensor is often installed inside the door lock actuator but can sometimes be installed externally from the lock.
To find the faulty door latch sensor can be tricky if it just happens sometimes, though.
A door latch sensor usually has two wires to it, which are open circuit when the door is open or closed circuit when the door is closed or vice versa. This makes it easy to measure with a multimeter.
The door actuators are often located inside the door, though, so it might be a little bit difficult to measure if you do not measure from the control unit instead.
Faulty Key Fob
The key fob, also known as a car remote key, is a device used to lock/unlock your car doors and even start the engine with just a push of a button.
Since the key fob also has controls linked with the car alarm system, a malfunctioning or faulty key fob can send an incorrect signal, which may trigger the car’s alarm.
You can check and replace the essential key fob batteries or reset the device to fix the problem. When you have replaced the batteries, and you have communication problems, you may have to reprogram your key fobs in some situations.
Incorrect Installation of the Alarm
If you have recently installed a new car alarm system and noticed that the alarm keeps going off for no reason, it may be because of incorrect installation.
If you let a mechanic workshop install it, go back and explain your problem, and if you installed it by yourself, it is time to recheck the installation manual and double-check everything.
Bad Alarm Control Module
Car alarms installed from the factory often have an integrated alarm control unit and a main electric component control unit, so a faulty control module is not common.
An aftermarket car alarm often has an alarm control module that controls all sensors and switches; if this control module fails, it may cause the car alarm to go off now and then.
Hi, I’m Magnus, the owner and the writer of Mechanic Base. I have been working with cars for 10 years, specialized in diagnostics and troubleshooting. I created this blog because I was tired of finding false information on the web while looking for repair information. I hope you enjoy my content!