Car Alarm Keeps Going Off: Common Reasons and Possible Fixes

Your car's alarm is one of its most important safety and security features. It tells you and others around your vehicle if there is any suspicious activity or attempted break-ins. And it's quite loud, so it's impossible to miss.

But that's precisely why it can be so frustrating when your car alarm keeps going off for seemingly no reason. Not only is it annoying to you and those around you, but it can also drain your car battery and potentially lead to a malfunction in the alarm system.

Fortunately, there are some common reasons why this might happen and potential fixes that can help alleviate the issue.

Why does my car alarm keep going off randomly?

When your car alarm keeps going off randomly, it's because of one of three things: user error, environmental factors, or an issue with the alarm system itself.

Car alarm systems work by detecting changes in the environment around the vehicle. This includes movement, sound, or even changes in temperature. If your alarm system is overly sensitive or there are other factors at play, that's what causes false alarms.

Common triggers for false car alarms

Believe it or not, there are actually several reasons your car might be triggering its alarm without any apparent cause. The most common issues are:

• Faulty alarm system
• Low or faulty car battery
• Faulty key fob
• Sensitive shock or motion sensors
• Corroded or loose wiring
• Hood latch sensors
• Environmental factors

Let's dive into each issue and how to potentially fix it.

Faulty alarm system

Of course, the main reason your alarm could be going off at random is the system itself. Maybe it isn't working properly due to a manufacturing defect or age-related wear and tear. An internal fault within the system’s control module can cause it to trigger erroneously.

Fix: If the alarm system is old or has been causing frequent issues, it might be time to have it inspected by a professional. In some cases, replacing the alarm system may be necessary.

Low or faulty car battery

The car battery plays a crucial role in the functioning of the alarm system. The system relies on a stable power source to monitor the vehicle's surroundings and respond to stimuli, and a low or malfunctioning car battery will have a lower voltage. If the voltage drops below a certain threshold, it can cause the alarm to go off because the alarm system interprets the voltage drop as tampering.

Fix: Check your car battery's health and charge levels. If the battery is old, failing, or shows signs of corrosion, replacing it could solve the problem.

Faulty key fob

The key fob might be malfunctioning due to a weak battery or internal electronic issues. If the fob is sending erratic signals, it can trigger the alarm unexpectedly.
This is common when the fob is dropped or exposed to water, causing damage.

Fix: Replace the key fob battery and ensure the fob is not damaged. If the problem persists, consider getting a new key fob.

Sensitive shock or motion sensors

Car alarms are equipped with sensors to detect motion, vibrations, and impacts. Functionally speaking, this is for detecting forced entry or vandalism. If the sensors are too sensitive or poorly calibrated, they can trigger false alarms for events that aren't actually a threat. Even minor disturbances, like a passing car or gust of wind, can set them off.

Fix: Adjust the sensitivity of the sensors. You might need to consult your car’s manual or take the vehicle to a mechanic who can recalibrate the alarm system.

Corroded or loose wiring

Over time, the wiring connected to the alarm system can become corroded or loose. This can cause intermittent connections, leading to random alarms.

For example, a corroded wire can send a false electrical signal to the alarm system, which triggers it. Similarly, loose wiring can cause the alarm to go off when the car is shaken or moved slightly.

Fix: Inspect the wiring for any visible damage, corrosion, or loose connections. Repairing or replacing faulty wires should stop the false alarms.

Hood latch sensors

Most cars (particularly those with a hood release latch inside the vehicle) have a sensor that detects when the hood is opened to prevent tampering.  If these sensors are dirty, misaligned, or faulty, they can cause the alarm to go off when it isn't supposed to.

Fix: Clean the hood latch and sensor area thoroughly and ensure the sensor is correctly aligned. If the issue persists, you may need to replace the sensor.

Environmental factors

Extreme temperatures, heavy rain, and other environmental conditions can sometimes cause the alarm to malfunction.

For example, if your car is parked outside, condensation and moisture in the air can trigger the alarm sensors. The same can happen if it's been sitting in the sun on a hot summer day, or when the air outside is below freezing.

Fix: While you can't control the local weather, you should still keep your car protected from extreme weather conditions as much as possible. If you live in an area with harsh weather, consider investing in a waterproof and shock-resistant alarm system.

Resetting your car's alarm system

Usually, resetting your alarm will solve the issue (at least for the time being). The process for resetting the alarm will vary depending on your car's make and model, but it typically involves pressing a combination of buttons or using a key fob sequence.

Here's a step-by-step guide to walk you through it:

1. Lock and unlock the car with your key fob.

Method: Start by using your key fob to lock and then unlock the car. The locking/unlocking sequence sends a signal to the alarm system, which can help recalibrate or reset it.

Believe it or not, this is often enough to reset the alarm system.

If the fob isn't working, try replacing the battery and then repeat this step.

2. Use the ignition key.

Method: Insert the key into the ignition and turn it to the "ON" position (do not start the engine). Leave it in this position for about 10 to 15 minutes. Then, turn it back to the "OFF" position and remove the key.

This process can reset the electronic control unit (ECU) or the alarm system's control module by cutting off power temporarily.

For this to work, make sure all doors, bonnet, and boot are properly closed during this process.

3. Disconnect and reconnect the car battery.

Disconnect the negative terminal of the car battery and leave it disconnected for about 15 minutes. Reconnect the terminal after waiting and double-check it's securely fastened.

This works because disconnecting the battery cuts power to the alarm system, effectively resetting it when power is restored. Keep in mind, though, you may need to re-enter radio codes or reset other electronic settings in the vehicle after doing this.

4. Reset the alarm using the 'alarm override' button.

Some vehicles have an alarm override button or switch located under the dashboard, by the fuse box, or near the steering column. It's designed to manually reset the alarm system in case of malfunctions. If your car has one, the button is often small and may require a pen or similar object to press.

Locate the button using your vehicle’s manual. Press and hold it while turning the ignition key to the "ON" position.

5. Check for a factory reset option.

Some cars have a factory reset option for the alarm system, which you can access via the car's infotainment system or by following a specific sequence of steps outlined in the vehicle’s manual.

A factory reset will restore the alarm system to its original settings, which will clear any faults (provided they aren't related to physical damage or faulty components).

Tip: Be cautious with this option, as it will probably erase other settings in the car

Testing your car alarm to ensure it’s working properly

After performing the reset, lock and unlock the car using the key fob or manually to test if the alarm system is functioning correctly.

If your car doesn't let off a sound when you lock it to indicate the alarm is active, you can also have someone get into the car while you lock it. When they open the door to exit the vehicle while the alarm is activated, it should go off.

Temporarily disabling your car alarm

Most factory-installed car alarms are programmed to deactivate when the corresponding key or key fob is nearby. A common way to disable your car alarm is by inserting your key into the door lock on the driver's side, locking it, and then unlocking it.

You can also use the methods mentioned above, which involve turning off the car or disconnecting the battery, to temporarily disable your car alarm.

Remember, though, that these methods are for temporary disabling. The alarm will reactivate when the vehicle is locked or started again.

DIY fixes for a faulty car alarm

Besides the steps mentioned above, there are several DIY fixes you can try before taking it into the garage.
Here are a few things you can try:

1. Replace the key fob battery.

A weak or dead battery in your key fob can cause the alarm to malfunction, triggering it randomly or preventing it from deactivating.

Replace the battery in your key fob with a new one. Most key fobs use a standard coin battery (like CR2032), which is easily replaceable. After replacing the battery, try locking and unlocking the car to see if the problem is resolved.

2. Check the door, bonnet, and boot sensors.

Faulty or misaligned sensors on the doors, bonnet, and/or boot trigger the alarm to trigger when it isn't supposed to make a sound. These sensors detect when someone is trying to get into the car, but malfunction if they get dirty or corroded or have an alignment issue.

Inspect all the sensors for these issues. Even if an issue isn't immediately obvious, clean them with a soft cloth and some electrical contact cleaner. Make sure they're properly configured as well. If a sensor is damaged, you'll need to replace it to fully fix the issue.

3. Inspect and tighten the battery connections

Loose or corroded battery terminals sometimes cause voltage fluctuations that trigger the alarm. To rule this issue out, open the bonnet and inspect the battery terminals.

If they appear loose, tighten them with a wrench. If you notice corrosion, clean the terminals with a mixture of baking soda and water, then rinse and dry thoroughly before reconnecting.

4. Adjust the alarm sensitivity.

If your shock sensors are overly sensitive, they might be triggered by minor vibrations, louder vehicles passing by, or even natural events like a strong gust of wind or heavy rainfall.

Lots of alarm systems allow you to adjust the sensitivity settings. Check your manual to see if this is possible.

The adjustment is usually made via an adjustment dial or switch on the alarm module, which might be located under the dashboard or in the engine bay.

5. Reset the alarm system.

Software glitches in the alarm system can cause it to act unpredictably, even when there's nothing wrong with the car itself. Resetting the alarm system can fix this.

To clear a potential glitch, disconnect the car battery for 10-15 minutes and then reconnect it. Alternatively, some vehicles have a specific reset procedure detailed in the owner's manual.

6. Check for faulty wiring.

In our experience, sometimes it’s damaged or loose wiring within the alarm system that leads to false alarms. Examine the wiring connected to the alarm system, especially around the battery and the alarm control unit.

Inspect for any signs of wear, corrosion, or loose connections. Secure any loose wires and replace damaged sections if necessary.

7. Lubricate the door locks.

Sticky or stiff door locks can sometimes cause the alarm to think the vehicle is being tampered with.

Use a graphite-based lubricant or a silicone spray to lubricate the door locks. Avoid using oil-based lubricants as they can attract dirt and grime, leading to more problems over time.

What should I check if my car alarm goes off at night?

If your car alarm keeps going off at night, there are a few things you can check to try and stop it from happening:

• Make sure all windows and doors are closed properly.
• Check the hood and trunk to make sure they're securely closed.
• Inspect the sensors for any obstructions or damage.
• Consider the weather, is it below freezing or windy outside? These conditions can trigger the alarm.
• Park your car in a different location or angle it differently to see if that makes a difference.
• Verify your car isn't overly sensitive to louder vehicles passing at night.
• Look around for animals at night that could be setting it off.

When should I seek professional help for my car alarm?

If the reset steps and DIY fixes don’t resolve the issue, you will need to consult a professional mechanic or visit your dealership. Persistent problems could indicate a deeper issue with the alarm system’s sensors, wiring, or control module.

You should also seek professional help if you find that the issue is related to a malfunctioning part. You'll need to replace the faulty part, so it's best to have a trained mechanic properly diagnose and fix the problem.

Just selling your car for scrap? No need to fix the alarm beforehand. We buy cars in any condition.

What are the signs of a failing car alarm sensor?

There are a few signs that could indicate a problem with your car alarm sensor:

• It goes off without any apparent reason.
• It activates when it shouldn’t, and/or fails to activate when it should.
• The dashboard warning light indicates an issue with the security system.
• You purposely test the alarm by shaking the car, opening a door, or tapping a window, and the alarm doesn’t activate.
• The alarm triggers with minor disturbances, such as a light touch or small vibrations that wouldn’t normally set it off.
• The alarm doesn’t disarm as it should when you unlock your car using the key fob.
• Your car battery is draining unusually quickly.

If you notice any of these signs, have your vehicle inspected by a professional. Diagnosing and fixing a failing sensor is what prevents unnecessary disruptions and ensures your car's alarm system is functioning properly.

Are there specific models known for alarm issues?

Certain car models in the UK have been reported to experience more frequent alarm issues than others, for one reason or another. Issues can range from overly sensitive sensors to faults in the alarm control unit

A few examples:

• Hyundai ix35: This model has been noted for alarm issues, particularly related to its Anti-lock Brake System (ABS) modules. Faulty ABS modules can sometimes cause electrical shorts that may trigger the alarm unexpectedly. There have also been reports of other electrical issues in this model that could affect the alarm system​.
• Kia EV6: Owners reported alarm issues with early versions of the Kia EV6, with the system going off randomly, often due to overly sensitive internal sensors. This problem seems to have been more prevalent in earlier models, and it was addressed by replacing the faulty sensors.
• Nissan Qashqai: Although not as widely reported as the Hyundai ix35 or Kia EV6, some Nissan Qashqai owners have noted issues with their alarms going off without reason, often linked to sensor faults or battery-related problems.

Keep in mind that plenty of cars will experience alarm issues from time to time, so it's not necessarily a reflection of the entire model range.

To sum it all up

Dealing with a car alarm that won't stop going off is frustrating, especially if it's bugging your neighbors or creating unnecessary stress for you.

Start by checking basic things like the key fob battery, sensitivity settings, and potential glitches in the system. If those steps don't work, it may be time to seek professional help or replace certain parts of your car's alarm system.

By taking the steps outlined in our guide, you should be able to fix most of the issues. But if it's a problem with the wiring or faulty equipment, you'll need to take it to the garage for work.

By addressing these issues promptly, you can ensure your car's security system is functioning properly and avoid unnecessary disruptions in the future.