Why does my car alarm keep going off? 4 Reasons

If you find your car alarm keeps going off, and it's not the result of theft or tampering, there are a few possible reasons, from faulty electrics to wandering insects.

Let’s take a look at what can cause your car alarm to trigger randomly and, more importantly, what you can do to stop it.

What triggers a car alarm? 4 Common culprits

First off, if you hear the sound of your car alarm, don't ignore it. It's always a good idea to make sure that nothing is wrong. Be sure to do so safely, perhaps from a distance initially, to ensure you don't walk into a dangerous situation.

Once you know that someone isn’t trying to get into your car, consider whether one of the following common culprits of random alarm activations is to blame: 

1. Your key fob: Your key fob remote controller transmits a signal to a receiver in your car to either lock or unlock it. If the battery in your remote key fob is low or there are any faults within the mechanism itself, it might not send the correct signal to the receiver. Any problems with this signal may be interpreted by your alarm system as an unauthorised entry and trigger the alarm, even if your car is perfectly safe.
2. Trigger-happy sensors: An alarm that triggers without obvious cause could simply be a result of its sensors reacting to the environment. A passing pedestrian bumping your car, or strong weather like wind or rain, can trigger your car's alarm sensors if the sensitivity is set too high. Even an insect flying around the inside of your car can set your alarm off by activating the car's internal motion sensors.
3. A faulty alarm system: In many cases, a car alarm that regularly goes off unnecessarily does so because of a faulty system. If newly installed, random alarm activations could be the result of poor installation. Whereas in an older system, dirty or malfunctioning sensors could be to blame. 
4. A fault with the vehicle: Finally, an unexplained car alarm can be the result of issues with the car itself. A fault with your car battery or alternator (which is responsible for charging the battery and supplying electricity to the rest of the car) can trigger the alarm, as can something as simple as a loose connection. 

How do I stop my car alarm from going off randomly?

A car alarm that repeatedly sounds is not only annoying but can land you in hot water with your neighbours. Let's take a look at a few things you can try to ensure your alarm functions properly.

If you suspect the key fob

• Replacing the battery in your remote key may be all that's needed to stop your alarm from triggering randomly. If your alarm siren is sounding, and you are in range of the car but still unable to switch it off by pressing the “lock” and then “unlock” button, it may be that the key fob batteries need replacing.
• Loose or worn-out buttons on the remote unit can also cause your alarm remote signal to malfunction. Luckily, depending on the make and model of your car, these can often be ordered online and replaced at home. 

• If you replace the battery and any loose buttons, and your alarm is still triggering randomly, you may need to have the remote reprogrammed by your local auto locksmith or even replaced entirely. 

The Master Locksmiths Association, which is the UK's largest trade association for locksmiths, has a list of qualified, vetted, and inspected locksmiths near you.

If sensor problems might be the root cause

1) Be sure to close all your windows tightly when you exit your vehicle to prevent wayward creatures from getting inside and setting off your car’s internal motion sensors.

2) Adjust the sensitivity of your alarm sensors. If you suspect strong winds or pelting rain are setting off your alarm, you might have overly sensitive shock sensors. These are the sensors that respond to any physical impact, such as a thief tampering aggressively with the locks. 

Some cars are also fitted with microphone sensors, which are designed to detect sudden changes to the ambient sound level around your car, like a window breaking. These can be triggered by thunder or other loud noises. 

Depending on the make and model of your car it may be possible to adjust the sensitivity of these sensors yourself. If so, you’ll find detailed instructions in your owner's manual. But if yours isn’t a DIY-friendly situation, or you're not confident to try, a quick trip to your local auto electrician may be your best option. 

In either case, it's important to find a good balance between reducing the sensitivity just enough to limit false activations while still keeping your car safe.

3) Make sure your sensors are clean and in good nick. Dirt, dust, and grime build up between sensors can prevent the alarm’s circuit from completing properly and so trigger the alarm. Fortunately a soft cloth and mild car shampoo may be all that's needed to clean and restore the proper connection between sensors. Your sensors can usually be found on the door edges, and bonnet and boot latches.

If it's a case of faulty or misaligned sensors on the other hand, you may be able to check and replace them yourself. This will of course depend on the make and model of your car as well as how handy you are. 

Electrical faults and defective alarm systems

When it comes to electrical faults, some can be dealt with at home, but others may need professional help to diagnose and properly repair or replace the malfunctioning part. 

• Check your car battery health. The low voltage of a drained and dying car battery can trigger a car alarm, as can corroded or oxidised battery terminals. So if your car alarm goes off through the night and the next morning your car battery is dead, it's probably that same battery that has been the source of your car alarm woes.

Remember, a standard 12V car battery only usually lasts three to five years. If the age of your battery is still within those parameters, you could check that the terminals are clear and in good condition. If not, a good clean with battery cleaner may be all that's needed to ensure a proper connection between your battery and your alarm.

• Electronic defects are a common cause of malfunctioning car alarms. General wear and tear, or even poor workmanship can result in damage to the many wires and cables that make up your car's electronics. This is one of the causes of a faulty alarm system that will probably need to be dealt with by a professional. The Motor Ombudsman has an online directory of recommended UK garages you can search by service and postcode. 
• Incorrectly installed aftermarket car alarm systems. If yours is an aftermarket alarm system, in other words one installed after the car left the factory floor, it may be worth double checking that the system has been correctly installed. 

If you installed the system yourself, refer to the installation instructions to ensure that all the steps were followed correctly. If you had a third party install the system, you can take it back to them and run them through the issues you're experiencing and they may be able to help. 

How do you fix a car alarm that won't stop? 

You can be fined by your local council if your car alarm sounds constantly for more than 20 minutes or an hour intermittently. So what can you do to fix a car alarm that won't stop, even after trying to switch it off with your remote? 

1. First off, if you have a traditional car key, you may be able to unlock the driver's car door manually, and so stop the alarm and potentially reset the alarm settings. 
2. Next, if you're unable to deactivate the alarm siren this way, check your car manual for any troubleshooting advice it may contain on malfunctioning alarms. 

• • This could be as simple as putting your key into the ignition and turning on the car, thereby signalling that the rightful owner has gained entry and not a thief.

• • Newer aftermarket systems may have an alarm switch on your car's dashboard marked “off”. 

• • Some will need you to complete a certain sequence to stop and reset the alarm: for example, pushing the alarm’s “on” button while pressing your foot on the accelerator and turning the key into the on position in the ignition. A beep or other sound will usually alert you that the system has been reset.

3. Then, if none of the above options stop the alarm from sounding, you could consider locating the fuse box and removing the alarm fuse with a pair of pliers. Each car fuse sends power to a particular car part.

• • Most cars have their fuse boxes located either in the engine compartment, under the steering wheel or in the cubby hole. The owner's manual should tell you where to find and access the alarm fuse. 

• • If you are unsure which fuse it is, you may have to go through removing and replacing the fuses one at a time to find the right one. You'll know you've found it when the alarm is silent. 

4. Finally, you might decide to disconnect and then reconnect the car's battery. 

• • Some cars require specialised equipment to do this but in most cases you should be able to do this at home. Removing the negative terminal on your car battery, which will be marked with a negative (minus) for around 40 minutes before reattaching it, should reset the battery entirely. 

• • However it's important to know that this can also reset other electrical and infotainment systems within your car, so you may want to check in with your car's garage for advice beforehand.

• • Some alarms also have a backup battery. If the alarm continues to sound after disconnecting the main car battery and you can't locate the backup, it should not go for long before running out of juice. After that, it might be worth heading to an auto electrician for help.

How to disable a car alarm permanently

Depending on the make and model of your car and the type of alarm system installed, consider removing the alarm fuse for good to disable it permanently. 

You could also disconnect the car's battery, although, of course, this will also disable the car. So this is only really an option if you are not planning on using the car or to stop your alarm from triggering during the night-time hours.

It's important to note though, that disabling your alarm could affect your insurance coverage should your car be broken into. And of course, it may make the car easier to burgle. In addition, some car alarms are connected to the car's immobiliser system, which means that once disconnected, the car won't start. If in any doubt, it's best to consult a professional.

Instead of an alarm, you could consider alternative security measures such as wheel and brake locks, tyre clamps, and/or trackers to protect your car. You might also consider video options such as dash cams, CCTV surveillance, or motion-activated doorbell alarms. But remember to notify your insurer of any changes if you do.

Key takeaways

A car alarm that keeps going off could be an issue with your key remote, over-sensitive sensors, a faulty alarm system, or an electrical problem with the car itself. 

It may be something that can be easily dealt with at home with the right tools and know-how. But if you continue to experience persistent false alarms or if there is any physical damage to the system, it might be best to check in with your alarm provider or an auto electrician.

Remember, a properly functioning alarm is an important part of your car's security system and is likely to have an impact on your car insurance coverage. So before making any changes, be sure to check in with your insurer.

At Howden, we take your needs into account, and recommend insurance policies that fit your individual circumstances. Contact us today to find the best coverage for your car.

Also read:

• Which areas are most affected by car theft?
• Thieves target keyless entry cars
• Lost car keys? Here’s what to do
• CAR INSURANCE GUIDES