A car alarm is an excellent way to protect your vehicle. It lessens the likelihood of losing your car to a thief. However, sometimes they can start going off for no reason, leading the owner to wonder “why does my car alarm keep going off?”.
This can quickly become a nightmare for the owner, especially when the annoying noise becomes somewhat of a nuisance in the neighborhood.
So, why does your car alarm keep going off?
The most common reasons that a car alarm would keep going off are:
- Faulty hood latch or door sensors
- A low battery
- A defective key fob
In this article we will look in detail at what sets off a car alarm, why an alarm would keep going off for no reason, and what you can do about it.
What is the function of a car alarm?
A car alarm protects your car from criminals. With sensors installed in different parts of the vehicle, the role of the alarm is to alert you of any unauthorized access or movements around your car.
With a good alarm system installed in your vehicle, it lessens the chance of a thief stealing your car.
What triggers a car alarm to go off?
A range of sensors are installed in vehicles that are used to trigger the car alarm. These sensors are designed to detect any unusual movements, vibrations or sounds in the vicinity of your car.
Sensors are like the nerve cells of a car alarm system. Modern vehicles have onboard computers that collect information from the sensors around the car, along with a receiver that allows the alarm to be armed and disarmed from an isolated key fob.
If the alarm is armed and the sensors detect something amiss, such as a drop in voltage, the trunk being forced open, or the car being lifted by a tow truck, the computer reacts by triggering the alarm.
Some alarm systems even have a backup power source if a thief disconnects the battery to attempt a silent escape.
Modern alarm systems can include a multitude of sensors, with each differing in function to keep your car safe. They include:
Door Lock Sensors
The door is the most common way to access to a car. So, it is no surprise that the door (including the hood, trunk, and latch) sensors are the most utilized sensors in alarm systems.
If someone tries to open the door forcefully when the alarm is armed, it will go off.
Some criminals have resorted to towing vehicles away in an attempt to bypass the alarm.
Tilt sensors keep a check on the car’s position by detecting a change in its orientation. If someone tries to tow the vehicle or lift it onto a flatbed, the alarm is sure to go off.
Impact sensors detect a sudden jolt to the bodywork or windows of a car. If the impact is strong enough, it triggers the alarm.
For instance, if someone tries to break into your vehicle by smashing the window.
Microphones inside the car are programmed to detect any irregular noise or disturbance in the environment. When they sense a loud sound, such as glass breaking, it triggers the alarm to go off.
This is why car alarms will sometimes sound when there is an accident nearby, or an explosion in the vicinity.
Proximity sensors help the car’s computer determine how close an object is to the car. The area around the vehicle is scoured to pick up any object or person that is too close, which triggers the alarm if it is closer than the defined range.
Why would a car alarm go off for no reason?
Car alarms are designed to go off for when the vehicle’s safety is likely to be compromised.
But what if your car alarm keeps going off randomly, even when your car isn’t in danger of being stolen or damaged? Here are some reasons why your car alarm would keep going off for no reason:
A faulty key fob
A key fob is a small isolated control device that allows you access to your car without physically unlocking your car.
A key fob that is programmed incorrectly, or has had its battery drained of power, can confuse the car’s alarm system and keep setting the alarm off.
A dirty hood latch sensor
The hood latch sensor is designed to detect if the hood has been opened while the vehicle is locked. But as it’s usually at the front of the car, it’s often exposed to debris.
If there is dirt blocking the sensor, the car’s alarm system may conclude that the hood is open even if it isn’t, and will sound the alarm.
As well as alerting the car owner to potential thieves, the alarm system also detects when something is wrong with the car battery.
If the alarm detects a low battery voltage, it will keep going off to alert you. If this is the case, it’s likely to go off when you first start the car, but can also go off at random times.
Dirty or rusty battery terminals
It’s not only when the battery is on its last legs that it can cause the alarm to go off. If the terminals are in poor condition, it can lead to reduced power levels which tricks the system into thinking the battery is low.
Some people aren’t happy with the alarm system that was installed from the factory, so opt to install an aftermarket solution.
This is a great way to further protect your car, but if the installation isn’t done correctly it is likely to lead to the alarm going off for no reason.
An alarm system can be very sensitive, so if the installer fails to correctly test the system for faults, it can be prone to false alarms.
Faulty door lock or trunk sensors
Just like the hood sensors, door and trunk sensors can also malfunction thanks to a build up of dirt, or from water ingress.
If the sensors are faulty or damaged they are likely to continue sending incorrect information to the computer, and this will keep your car alarm going off.
A car’s electronic systems can be extremely complicated with plenty of wiring that has the potential to go wrong. The alarm system is no exception.
If there is a problem with the alarm’s wiring, the signals may become disrupted. Wiring can degrade over time, or become damaged by moisture.
If this happens, the onboard computer may mistake the disrupted signals for threats and keep sounding the alarm.
Overly sensitive shock sensor
Sometimes, shock sensors can be programmed incorrectly and be triggered with even the slightest touch.
Some sensors are just more sensitive than others, but others could have been incorrectly calibrated.
Why would a car alarm go off in the middle of the night?
A car alarm sounding in the middle of the night is not only annoying for you, but also for your neighbors. It’s even worse if it keeps happening, and you may find yourself with a number of complaints.
But why would a car alarm go off in the middle of the night? It could mean one of several things:
The alarm system has an issue that needs resolving
The most common reason for a car alarm to keep sounding in the middle of the night is that the alarm system has an issue that needs a solution.
It could be any of the issues we’ve mentioned above, but the most common is the low battery warning. This could be because the battery is genuinely low on power, or the terminals are not making good contact with the battery.
Thieves often operate in the dead of night to minimize the number of potential witnesses to their crimes. If you suddenly hear your car alarm going off in the night, thieves could be targetting it.
They could steal the car in a number of ways, but generally at night they will try to make the quietest possible getaway. This could involve towing the car, lifting it onto a flatbed truck, or trying to gain access with a stolen or cloned key.
Unfortunately it’s not only thieves that car alarms have to protect against, it’s also vandals. All too often people have woken up to find their car alarm going off, only to discover the cause is a vandal throwing rocks or bricks at it.
This is more common in areas where street parking is the norm, but could happen anywhere.
If your shock sensors are programmed to catch even the tiniest touches, then it’s likely you’ll be getting plenty of alerts at night.
For instance, your car alarm could go off if a cat or other nocturnal animal climbs onto your vehicle or brushes against your door. If there is a storm overnight, strong winds can also cause your alarm to keep going off.
How do you turn off a car alarm?
If your car alarm is going off and the vehicle isn’t being stolen or damaged, you’re going to need to turn it off. Here’s how:
Use the lock or unlock buttons: The simplest way is to press the unlock / lock buttons on your key fob to make the alarm stop. You can use the physical key if the remote key doesn’t work.
Start your car: If the alarm is still going off once you’ve unlocked the vehicle, usually starting it is enough to stop your alarm.
How do you fix a car alarm that keeps going off?
If your car alarm keeps going off and the previous solutions haven’t worked, there are some other things you could try.
Reset the alarm
Car alarms can usually be reset, but the process is different for each type of car. Consult the user manual or utilize online forums dedicated to your particular car to figure out how to reset the system. A simple reset will often solve the issue.
Try diagnosing the problem yourself
If you don’t mind getting your hands dirty, you could try diagnosing and fixing the problem yourself, keeping in mind the common causes of a faulty car alarm we mentioned earlier.
Faulty key fob: Get your key fob re-programmed by a dealer or car locksmith.
Dirty hood, trunk, or door sensors: Clean any dirt, oil, or gunk off your latches using a soft cloth. If the problem continues, you may need to get the sensor changed.
Low battery: check the voltage of the battery using a multimeter. If it’s below 12.6 volts, you may need to get it replaced.
Dirty or rusted battery terminals: If you notice any dirt on the terminals, disconnect the battery and clean them properly. Take care doing this to avoid damaging the battery; there are plenty of online guides detailing how to clean car battery terminals.
Poor installation: Take it back to the original installer and ask them to fix it, or take it to an independent auto-alarm specialist.
Overly sensitive shock sensor: There is usually a way to adjust the sensitivity of the shock sensor, and in many cars the owner is able to do this without consulting a professional. Be sure to consult the owner’s manual for your particular vehicle.
Have your car alarm checked
If you’ve reset the system and checked the common issues yourself, but the car alarm continues to sound, take your car to a mechanic or alarm specialist. They will be able to diagnose the fault and let you know what’s needed to fix it.
If you can’t get to a garage straight away, there are some other temporary solutions to stop the alarm going off and annoying your neighbors:
Remove the fuse: If your alarm keeps going off and you need to disable it until you get it fixed, you can remove the fuse to cut off the power supply. But be aware of the security implications of doing this, and potential insurance issues.
Doing this automatically stops the noise as the alarm isn’t receiving any power. Check the owner’s manual to find out which fuse to remove.
Disconnect the battery: This should be your last resort when everything else fails to work. Only do this if you are confident you know how to safely disconnect a car battery.
However, note that it may continue to go off if a backup power supply is available. It might not stop until the backup power supply is drained.
Of course, this step means you will no longer be able to drive the vehicle until you reconnect the battery.
We’ve investigated why car alarms sometimes go off for no reason, and provided a range of solutions to this problem.
These include resetting the alarm, diagnosing the problem yourself, or taking it to a mechanic.
While it is often possible to diagnose the issue yourself, alarm systems can be complicated and it’s extremely frustrating when the cause of the problem can’t be identified.
If all else fails, there are ways to temporarily disable the alarm until you can get the car looked at by a professional.