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My car alarm keeps going off. What should I do?

If your car alarm keeps going off for seemingly no reason, it can be a stressful nuisance and you’ll want to identify the cause and stop it quickly.

We look at some common reasons your car alarm could be acting up and how to fix them, including how to turn off your car alarm if it won’t stop going off.

If your car alarm keeps going off for seemingly no reason, it can be a stressful nuisance and you’ll want to identify the cause and stop it quickly.

We look at some common reasons your car alarm could be acting up and how to fix them, including how to turn off your car alarm if it won’t stop going off.

Written by
Rory Reid
Car and technology expert
Last Updated
2 APRIL 2024
8 min read
Share article

Why are car alarms important?

Car alarms can help protect your car from theft by alerting you to the fact that someone is trying to break into your car. 

When a car alarm goes off, the loud noise and flashing lights are hard to ignore – and that’s the point. They’re designed to attract attention and deter any would-be car thieves from continuing to break in.  

Cars alarms are one of several security measures that could protect your car, such as parking in well-lit areas and using anti-theft devices like an immobiliser, steering wheel lock or GPS tracking device.

How do I know if my car has an alarm?

If you’ve never heard your car alarm go off, you may not be sure if your car even has one or if it’s working correctly. Here are a few ways to check whether your car has an alarm:

  • Check your car manual – it should include details on any alarm system fitted by the manufacturer.
  • Look for a light on the dashboard – some cars have a small LED light that flashes to show that the car’s alarm system is armed and ready.
  • Check your key fob – it might have a button you can press to activate the car alarm.
  • Ask at your next service – if you’re still not sure, you can always ask the mechanic next time you take your car in for its MOT or regular service. Alternatively, you could call up your local dealership and ask them.

Why does my car alarm keep going off?

Car alarms are not infallible and there are times when a particularly strong gust of wind, a violent hailstorm or a careless knock from a passer-by could set off the alarm unexpectedly. It may also be triggered if one of your car windows or doors isn’t properly closed. 

But when your car alarm keeps going off for no apparent reason it can be incredibly annoying, not just for you, but also your neighbours. 

The good news is that the cause could be easy to trace and, in some cases, there are quick ways to fix the problem – although depending on the problem, you may need to call in the help of a professional. 

Here are some of the most common reasons for a car alarm going off randomly

Key fob malfunction

One cause might be an entry key fob with a low or dead battery. Key fob batteries can go flat after long periods of use. If that happens, the fob might not be able to send signals correctly, which can cause the alarm to sound.

The solution? Swap the batteries out. Most fobs take the coin battery type, which can be bought from almost any shop that sells batteries. You should be able find out the exact type you need by looking in your owner’s manual.

The key fob itself should be easily opened with a screwdriver, so you can replace the battery without any issues.

If the battery’s not to blame, your key fob might need to be reset or scanned with a code reader. A car mechanic should be able to help.

Dirty bonnet latch sensor

In modern vehicles, the bonnet latch has a sensor that sets off the alarm if someone tries to force the bonnet open. Over time, dirt, grime and engine grease can build up and stop the sensor from working properly, occasionally triggering the alarm.

If cleaning the bonnet latch doesn’t solve the problem and you’ve checked for other solutions, it could mean a poor connection to the control unit, which will need to be fixed.

Poor installation

If you have an older car that didn’t come with a factory-fitted alarm, you – or the previous owner – may have installed an aftermarket alarm. Fitting a car alarm system yourself can save you money and help to lower your car insurance premium, but it’s easy to make mistakes with a DIY installation.

If an aftermarket alarm system wasn’t installed properly, or if one of the components has failed over time, this can lead to your car alarm going off randomly.

It’s also worth noting that failure to correctly install your alarm system could invalidate your insurance, so it might be worth getting it checked by a professional.

Low car battery

If your car battery’s running low and isn’t sending the right amount of voltage to the alarm system, it can set off the alarm. If your car battery is dead the morning after the alarm has been going off during the night, this is a likely culprit.

Even if the battery isn’t flat, rusty and worn-out battery terminals can also interfere with the flow of electricity.

You might want to start by giving your car a jump start and allowing your low battery to charge. Otherwise, the solution is simple: replace your old battery with a new one.

Dodgy sensors

Cars usually have a variety of sensors to detect activity. Door lock sensors, proximity sensors, tilt sensors, glass break sensors, shock sensors and microphone sensors, all help your car alarm detect when someone or something is trying to steal, get into or even tow your car.

If one of these sensors is faulty or overly sensitive, it can cause the alarm to sound.

A mechanic can use a scan tool to detect problems caused by faulty sensors, loose electrical connections or wiring issues that could be setting the car alarm off.

How to turn off a car alarm

If your car alarm has gone off in the middle of the night, there are a few easy steps you can take to silence the alarm sound immediately, although the solution will depend on your car and the type of car alarm system you have. Try the following:

  1. Lock/unlock the car doors. Push the button on the key fob or, if this doesn’t work, insert the physical key into the driver’s side door and lock/unlock the car. The physical key is usually tucked away inside the plastic key fob. The keyhole may also be hidden, often behind a cap or flap on the car’s door handle.
  2. Turn the car on. If opening the door doesn’t work, try moving the ignition to the on position or starting the engine. If the car allows it, this may silence your alarm – at least temporarily – while you figure out a more permanent solution.
  3. Turn the alarm off manually. There might be an ‘off’ button on the dashboard that you can push to manually turn the alarm off. If you can’t find anything, and the above steps haven’t worked, try checking your owner’s manual for specific instructions on how to deactivate the alarm.
  4. Kill the power. If all else fails, a last ditch option to disable your car alarm is to starve it of power by disconnecting the battery. One simple way of doing this is to remove the negative (black) battery connector from the battery.

    Be aware that if you do disconnect the battery, it could affect your car’s onboard computer and infotainment system. That’s why it’s more of a last resort.

What are the risks of turning off my car alarm?

If you disconnect your car alarm, you run the risk that your car will be easier to steal. With no alarm blaring to alert you, or your neighbours, to someone breaking in, someone could quietly steal your car in the night – or even in the middle of the day – without anyone noticing what’s happening. 

Not having a working car alarm could also impact or even invalidate your car insurance, meaning that you could have a problem making a claim if your car is then stolen.

What should I do if my car alarm keeps going off?

Persistent car alarm noise is not only a nuisance for you and your neighbours, it may also be considered a statutory nuisance by your local council. They could issue you with a notice and even forcibly remove the vehicle, charging you for any costs incurred.

So it’s best to get your alarm system checked by a qualified professional. If your car is fairly new and the alarm was factory fitted, it may still be covered by the manufacturer’s warranty. On the other hand, if it’s been fitted later by you or an unapproved mechanic, your warranty might be void.

Also, be aware that if your car alarm won't stop going off and is faulty, it could invalidate your insurance in the event of a claim.

Other ways to improve your car’s security

While car alarms can be a great deterrent for thieves, there are other ways you can improve your car’s security and avoid your car being stolen. Improving your car’s security features could help you find a lower price on your car insurance, too.

Here are some tips that might help reduce the risk of your car being stolen or vandalised:

  • If you want want an aftermarket alarm installed, invest in a Thatcham-approved car alarm and have it fitted by a qualified mechanic. Don’t forget to inform your insurance provider, as they may offer you a security discount.
  • Don’t just rely on your key fob. Always double-check that your car is locked before leaving it anywhere.
  • Don’t leave any belongings in view, even if your car is locked.
  • Take care of your keys and key fob. Many insurance providers offer key-care cover as an optional extra. This covers the costs of replacing lost or stolen keys as well as re-programming your alarm and immobiliser.
  • Make sure your car is parked securely overnight to minimise risk.

Anti-theft devices

There are other security devices that you could use alongside your car alarm to keep your car as safe as possible from thieves. These include:

  • Steering wheel and brake locks – these mechanical immobilisers disable the steering wheel and pedals.
  • Tyre clamps – prevent the car from being driven.
  • Faraday bags – a pouch to store keyless tech that blocks thieves from getting access to your car remotely.
  • GPS tracking devices – so you can see where your car has been taken if it’s stolen.
  • CCTV and doorbell alarms – capture any theft or attempted car theft on video.
  • Dashcams – can capture footage inside your car in case someone is able to break in.
Did you know?
Ferry companies usually insist you disable your car alarm when travelling with them, as vibrations from the deck can easily set off alarms during the crossing.

Compare and save

A high-quality, professionally fitted car alarm could help lower your car insurance premium. Another way to save money on your car insurance is to shop around.

Comparing quotes with us can be an easy way to find a deal that’s right for you.

Frequently asked questions

What is a Thatcham-approved car alarm?

A Thatcham-approved car alarm means that it has been rigorously tested and approved by Thatcham Research, an independent research body used by insurance providers as a benchmark for car security.

Thatcham-approved alarms and immobilisers are considered the highest quality and are trusted by car insurance providers, who often offer a discount if you have one fitted.

Can I disable my car alarm?

Your owner’s manual should have a section on how to disable your car alarm.

Most modern cars are fitted with an alarm system shut-off switch that lets you disable your car alarm. Your owner’s manual should tell you where it’s located.

What should I do if a neighbour’s car alarm keeps going off?

If a neighbour’s car alarm keeps going off and you’ve identified that it’s not someone trying to break in, your first port of call should be to go and talk to your neighbour. Let them know that it’s causing a nuisance and ask them to fix it.

If the problem continues, you should contact the environmental health team at your local council and they’ll take it from there.

On the other hand, if you suspect that someone’s actually trying to steal your neighbour’s car, call 999 immediately.

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