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

A car alarm not only helps protect your vehicle against theft and vandalism; in some cases it could help lower your car insurance premium.

However, 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.

A car alarm not only helps protect your vehicle against theft and vandalism; in some cases it could help lower your car insurance premium.

However, 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.

Written by
Rory Reid
Car and technology expert
Last Updated
6 MARCH 2023
5 min read
Share article

Why does my car alarm keep going off?

When your car alarm keeps going off for no apparent reason it can be incredibly annoying, not just for you, but also your neighbours. But the good news is that the cause is normally easy to trace and there are quick ways to fix the problem.

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

Key fob malfunction

One of the most common causes is 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. 

What’s the solution? Swap the batteries out. Most fobs take the coin battery type, which can be bought from almost any shop that sells batteries, and the fobs themselves can be pried open for easy battery replacement. If the battery’s not to blame, your key fob might need to be reset or scanned with a code reader. Your local 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, 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 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 you’ve failed to install an aftermarket alarm system properly, or if one of the components has failed over time, this can lead to the alarm going off when you least expect it. 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. 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. These can include door lock sensors, proximity sensors, tilt sensors, glass break sensors and microphone sensors, all of which can detect when someone or something is trying to steal, get into, or is already inside your car. If one of these sensors is faulty or is overly sensitive, it can cause the alarm to sound.

In some cases, it’s possible to deactivate or reduce the sensitivity on individual sensors so, if all else fails, take a look at your car manual and give this a go.

How do I turn off my car alarm? 

If your car alarm has gone off in the middle of the night, there are a few easy things you can do to silence the alarm sound immediately.

  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 door and lock/unlock the car. The physical key is usually tucked away inside the plastic key fob. You may need to locate the keyhole on the car’s door handle (often hidden behind a plastic flap) before this is possible.
  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. Some cars have their ignitions behind the push button starter (you can just pull the button off), but others will have their key holes in more unusual places.
  3. Turn the alarm off manually. If yours is an aftermarket alarm that you’ve had installed, you should be able to turn it off manually. If you can’t find the button or switch, look in the instruction manual.
  4. Kill the power. If all else fails, a great way to shut off 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 battery.

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 is faulty, it could invalidate your insurance in the event of a claim.

Improve your car’s security

The following tips could help reduce the risk of your car being stolen or vandalised:

  • If you want a post-market 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. 
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 could be the easiest way to find a cheaper deal. 

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?

Most modern cars are fitted with an alarm system shut-off switch. Your manual should tell you where it’s located, but it can often be found near the petrol cap or bonnet release.

That said, most makes and models will deactivate the alarm if you simply lock your car with a physical key rather than the fob. 

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

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

Obviously, if you suspect that someone’s trying to steal your neighbour’s car, call 999. But if they have a dodgy alarm that keeps going off, you should let them know that it’s causing a nuisance. 

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

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