After your car alarm has gone off in the middle of the night for the third time that week, no doubt waking you and your neighbours, it moves beyond irritating and into embarrassing. And in addition to disturbing those around you, a car alarm that's on the fritz could invalidate your car insurance. As if that wasn't bad enough, it could even result in a 'statutory nuisance' notice from your local council.

So, why does your car alarm keep going off? To help you get to the bottom of things, we'll take a closer look at the most common causes, as well as how to remedy the issues and keep those noisy nights to a minimum.

Why Car Alarms are Important

Car alarms still matter in this day and age. As a deterrent, the noise they create should soon have potential thieves scarpering. But a car alarm offers a number of other benefits too. An alarm system in your car can actually lower your car insurance premium, since insurers will take this into account when working out your overall insurance cost.

They also help when it’s time to sell on your car. A quality alarm system can increase the price, and let buyers know they can purchase with confidence knowing they can easily leave the car in a public space without worry.

Modern alarm systems work in conjunction with a smartphone app. In the event your car is stolen, you can send a signal from their phone that puts a stop to car’s functionality entirely – and thieves won’t be able to get very far when this happens.

Why Does my Car Alarm Keep Going Off?

Dead battery in key fob​

Your key fob contains a short-range radio transmitter that sends a distinct signal to a receiver unit inside your car. When it's in proper working order, it locks or unlocks doors and jumpstarts your car ignition at the press of a button. But when it's faulty, it's unable to send the signal to the receiver unit inside your vehicle, which causes your car alarm to go off for no reason.

How can I fix it?

In most cases, a new battery is enough to sort the problem. But there's a chance it may need to be reset too. Try taking it apart to see if there are any broken contacts or wonky buttons. If everything seems fine but your alarm is still going off, then you might need to reprogram the controller which you can do on your own or with the help of a professional.

Defective bonnet latch sensor

As well as your key fob, other sensors in your car might cause your car alarm to go off. Take your bonnet sensor, for instance. A fully functioning bonnet sensor picks up when your bonnet latch is open, closes the electrical switch and illuminates the dash with a warning light. When the bonnet sensor is defective, the car alarm goes off instead.

How can I fix it?

Since the sensor sits in the engine bay above the headlight frame, it tends to collect dirt, debris, and engine grease with ease, which causes it to trigger these false alarms. Giving the bonnet latch and sensor a clean can stop your alarm going off and protect your vehicle from theft and damage too.

A brake cleaner and cleaning brush will usually do the trick. If the alarm is still going off, then your bonnet may be damaged, or it may have been tampered with. If so, replace it as soon as you can.

​Poor bonnet latch connection

If your alarm is still going off after cleaning or replacing the bonnet latch sensor, then it could be an issue with the bonnet latch connection itself. Although it rarely happens, when it does you should take note. A faulty bonnet latch can also affect your car's control unit and lead to incorrect commands and reading, such as turning the airbag light on – even when there isn't a problem with the airbag function.

How can I fix it?

If there are no signs of damage, then disconnecting and reconnecting the bonnet latch connection usually sorts it. If not, then look for cable fraying or binding, setting of rubber stops on the bonnet, the condition of the pull handle assembly, or any wear or damage to the actual latch. Also, check to see if any of the levers or springs are worn out or bent. If so, you should have it looked at by a professional.

Faulty door lock sensor

The design of a car's door lock sensor means that rain can seep through the door lock actuator connector, which causes the car alarm to go off. Its internal wirings can also wear out and fail too.

How can I fix it?

Sealing the connector with protective grease and identifying the source of the leak fixes the issue. Keep an ear out for any buzzing or humming too, as this can help narrow down whether the door lock actuator is working or not.

In the case of faulty wiring, a scan tool can help determine which vehicle door has caused your vehicle alarm to keep going off the most. Whichever door it is, you should inspect the door lock connector and actuator to see if any of these parts require replacement.

Low car battery

If your car alarm goes off in the middle of the night and your car battery is dead the following morning, then the car battery is likely the main culprit. One of the main functions of a car alarm is to warn the driver about low battery levels. That's why turning the engine on with a dying battery will instantly set your car alarm off.

How can I fix it?

Using a voltmeter, check to see if its running voltage reads less than 12.6V (or whatever your owner's manual specifies). If so, you'll have to jumpstart, recharge or replace the battery.

Poorly installed alarm system

Factory alarm systems only provide a basic level of security and anti-theft protection, which is why many vehicle owners opt for an aftermarket car security solution. Unfortunately, that leads to improper installation, especially when motorists take the DIY route. If your car alarm keeps going off at night, then it could be because of the shoddy installation job.

How can you fix it?

If you tried installing it yourself, then double-check the instructions in the installation manual to make sure everything you did followed everything properly. If a professional installed it, then explain what's going on to them. A proper reinstallation of the alarm system will stop it from blaring away at night.

How Do I Turn off My Car Alarm?

Turning your car’s alarm off will depend on the type of alarm system in your car, as well as the make, model and age of the vehicle.

If your car key has a built-in remote, you may be able to turn off the alarm by unlocking the driver’s side door with the key rather than the remote.

Cars that have a button on the dashboard with the word ‘off’ on it can deactivate the alarm by pushing this button.

If neither of these things work, check the owner’s manual as it will more than likely have specific instructions on how to turn off the alarm. Refer to this if you’re unsure.

As an absolute last resort, if your car alarm is still going off, then you might have to disconnect the battery so you can reset the system. As we’ll explain later, however, we would advise against trying this.

More Car Alarm Questions: Answered

Why did my car go off in the middle of the night?

There’s nothing more irritating than your car alarm going off at night when you’re trying to sleep. If it keeps happening, and there’s nothing that suggests it might be thieves, then there may be a few other explanations for it.

A low battery can set your car’s alarm off. If you suspect this might be the case, then an auto parts shop may be able to test your battery for free – but you can easily test it yourself by connecting it to a voltmeter.

Animals perching on or near your car may by the culprit too. If this is the case, your alarm might be too sensitive. You can easily adjust the sensitivity of your alarm sensors, just be sure to check alarm owner’s manual to check how to do it.

If you’re parked on a main road, then large vehicles going by may be enough to set your alarm off too. Again, you may need to adjust the sensitivity of your alarm sensors.

My neighbour’s car alarm keeps going off – what should I do?

OK, so maybe there is something more irritating than your car alarm going off at night, and that’s your neighbour’s car alarm going off at night. It’s frustrating, but can you do anything about it?

Yes, you can. Obviously, you should start with letting them know about the repeated disturbances – politely and in an empathetic way. Chances are they probably know it’s been happening too, and let them know you’re offering to help resolve the problem together.

You should also keep a record of when, for how long and how frequently these incidents have been happening. This can help you and your neighbour determine what might’ve been triggering the alarm.

If that doesn’t work in resolving the issue, then you should get in touch with your local council. The record you kept will come in handy, as you can provide them with this evidence and request that they intervene. Local councils have to the power to issue warnings, fines and even to seize any vehicles that are repeatedly causing incidents.

If that still doesn’t work, and the noise is that severe and you can’t reach an amicable agreement with your neighbour, you might want to seek legal advice from a solicitor who specialises in noise disputes.

Should I disconnect my car alarm?

Disconnecting your car alarm should only be attempted as a last resort if you’ve tried everything else and you alarm is still blaring. Even so, we’d recommend against doing this since it may wipe your car’s onboard computer or infotainment system. Certain car models might not even let you disconnect without specialised tools – if this is the case, then we’d recommend getting it looked at by a specialist.

A word on statutory nuisances

In certain cases, a malfunctioning car alarm might be considered a 'statutory nuisance' by your local authority, especially if you live in a built-up area. When this happens, you might be issued with a warning notice, or even have your vehicle impounded, with any associated costs passed on to you.

If your factory-issue alarm has started to malfunction, then it's important to check to see if your warranty covers it. It's also worth investigating whether after-market alarms invalidate your warranty at all.

A malfunctioning alarm could also cause problems if you need to make a claim with your insurer for a break in or vandalism.

Anti-Theft Devices

You can safeguard your car even further by investing in anti-theft devices too. Here’s what we recommend:

-Faraday pouches: Keyless entry into cars means that thieves’ tactics to gain access to such vehicles have become more sophisticated too. A Faraday pouch is one way of combating these new methods. A small pouch with metalling lining, these nifty gizmos block your key’s signals from anywhere outside the bag, stopping thieves from copying your signals and stealing your car.

-Steering locks: Sometimes the oldest methods are the best. Steering locks not only stop thieves from being able to drive your car, but they’re a great visual deterrent too. They’re cheap as well, and certain designs mean that even if they manage to break the lock, thieves won’t be able to drive your car since the bottom section of the device will get in the way of their legs.

-Tyre clamps: For a more heavy duty device, then a tyre clamp sends a clear message: good luck trying to drive away with this attached. Tyre clamps stop any car in their tracks, so your car can’t be driven, pushed or towed away by anyone attempting to rob your vehicle. And if they attempt to remove the device, the time it takes to do so usually means they’re at a higher risk of getting caught too!

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