Why Does My Car Alarm Keep Going Off? Top Reasons and Solutions

If your car alarm keeps going off randomly without any apparent cause, it can be frustrating and disruptive to your neighbours.

(And well, worst case scenario, it happens in the middle of the night!)

This problem can be caused by issues with the various sensors that are designed to protect your car from break-ins, such as the latch, shock, tilt, pressure, proximity, and microphone sensors.

In many cases, the whole thing can be resolved by addressing minor problems, but it can also be a sign of more serious issues.

In this article, we will explore why your car alarm might be going off and how to fix it. If you have been asking yourself, “Why does my car alarm keep going off?” read on to find out more.

Reasons Your Car Alarm Keeps Going Off

Poor alarm installation

Cars come with Original Equipment Manufacturer (OEM) alarms, which are limited to one-way remote door locks and one-way remote start, as well as an injector killer connected to the horn trigger. These features provide basic protection, hence the need for enhanced aftermarket alarm systems. However, incorrect installation can leave you with an alarm that goes off randomly. You can fix this by returning it to the dealership for proper installation or hiring an expert.


Key fobs, especially those without a key on very modern cars, require the battery to be in 100% working condition for the vehicle to recognize the signal and unlock the car. If you manage to get into the car because it randomly worked once without the signal to switch the alarm’s immobilizer off, the car won’t start. But the car will recognize someone is sitting in it and potentially set the alarm off.

To fix this, you will start by ensuring that the key fob is clean and dry to prevent malfunction. You can change the battery if the problem persists, which is the most common problem with a key fob. If it doesn’t change, you can reset it by following the instructions in the user’s manual or contacting the aftermarket alarm manufacturer. 

Low car battery

The car’s alarm and other security features, like the alarm, are powered by the car’s battery. Some alarm systems have there own secondary battery, but this is usually limited to aftermarket retrofitted alarms. A low battery voltage will therefore trigger the alarm. In addition, corroded or rusted battery terminals can also trigger the alarm. This might happen when you try to turn the engine on while the battery is low.

Checking the voltage using a voltmeter would be best in this scenario. In most cases, the voltage should be above 12.4 volts, which indicates a good battery, and a reading below that calls for replacement or charging. 

Faulty control module

Modern cars come with Electronic Control Units (ECUs) controlling electric features such as fuel injection, cabin temperature control, and an alarm system. So, if the ECU is faulty, it will send the wrong signal to the alarm system, which will set it off. 

This problem often causes the car to stall, use too much gas, run poorly, and idle unpredictably. If your vehicle has any of these problems and random alarms, it will likely need to be plugged into a diagnostic system to check for a fault. The ECU will rarely cause alarm problems, but it occasionally happens.

Malfunctioning Door, Trunk, and Hood Latch Sensors 

All vehicles come with latches and small claws that release to allow the door, trunk, or hood to open and also, keep the doors locked when in motion. The latches have sensors beneath them to detect break-ins. When dirt and debris build-up on these latches, they can stop working and set off the alarm for no reason.

Most new cars will notify you on the dashboard if the door, hood, or trunk is open. Apart from giving the contacts a clean, there isn’t too much you can do apart from replacing the sensor if it fails.

Wiring issues

Since the car’s electric components are connected using wiring through relays and fuses any issues, such as water exposure and short-circuit, will send the wrong signals to the alarm and trigger it. Loose alarm wires can also lead to unnecessary signals. Fixing this problem is easy if you know your way around a car’s electrical system. 

Overly sensitive sensor

As the ultimate security precaution, new cars have sensors connected to most parts. For example, a microphone sensor can detect when a sound is broken, and proximity sensors can tell when someone is near the car. Some cars also come with tilt sensors to prevent the theft of catalytic converters. These sensors can malfunction, triggering the alarm.

This problem is straightforward to fix by resetting, but it’d be best to seek professional help because it’s not straightforward. It’s not even that easy to diagnose an overly sensitive sensor as the fault, even if the alarm is randomly going off.

How to Turn On the Alarm Should It Persist

Start the engine

start the car to turn off the alarm

Starting the engine will stop the alarm as it interrupts the signal. If the alarm doesn’t stop immediately, you should hold the key in place for about 30 seconds to let the security system detect that you have the right key. However, this is a temporary solution, and the alarm may go off soon after shutting down the engine. 

If the car key is push-button keyless ignition, the car may not recognize the sensor in the key if the battery is flat, so you may have to replace it or use the spare key to start the car.

Lock and unlock using theKeyfob

Using the key fob to unlock and lock the car will help the car’s security system find the proper signal and turn off the alarm. You should try unlocking the door using the physical key if it doesn’t work on the buttons. 

Unplug the fuse

The alarm system has a fuse that prevents excessive current flow. You can locate it in the car’s fuse box in the passenger compartment or under the steering wheel. It’d be best to unplug it if the alarm doesn’t stop after trying the first two methods. Alternatively, you can manually turn off the alarm, especially if it’s an aftermarket one. 

Disconnect the battery

Disconnecting the battery should be your last attempt if the alarm persists. Doing so cuts power from the control unit to the alarm system and shuts down the alarm. In most cases, this signals a serious underlying problem. Therefore, you should take the car to a mechanic.

Bottom Line

An alarm suddenly going off out of nowhere can be annoying and embarrassing. Fortunately, the problem can usually be fixed quickly, as discussed here.

Some of these problems are common in newer car models, but they shouldn’t worry you too much, as shutting the car alarm off usually requires very little car mechanical knowledge. However, it’d be best to take the vehicle to your nearest auto shop for a professional diagnostic test and repair if you aren’t sure of the problem.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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