Car Alarm Keeps Going Off (10 Reasons & How to Fix)

A car alarm going off all night is irritating, and when it’s your car, it’s embarrassing. Not only will it make you lose sleep, but it will anger the neighbors. Problems with your car’s alarm system can lead to a statutory nuisance notice. Worse, it could sway you from sensing when an actual intrusion happens.

Some of the reasons your car alarm keeps going off include faulty sensors, low battery, wiring problems, and a broken key fob. It could also be from unevenly closed doors. While an alarm or ECU reset can fix most issues, others may require professional services.

Determining what triggers the untimely wailing of your car alarm will help decide the right course of action to stop it permanently. Here are common reasons why a car alarm keeps going off:

  1. Nonfunctional key fob
  2. Defective hood latch sensor
  3. Poor hood latch connection
  4. Faulty door lock sensor
  5. Low battery level
  6. Corroded or rusted battery terminals
  7. Weak or overly sensitive sensor connection
  8. Disconnected circuitry or wiring problems
  9. Problematic control module
  10. Poorly installed alarm system

In addition to what’s on the list, remember the occasional bloopers like sitting on your key fob or unknowingly pressing the panic button (that color-coded red button with the alarm symbol) can set your alarm off. So, before you begin looking into the items above, make sure to rule out the obvious causes first.

10 Reasons Why Your Car Alarm Keeps Going Off

1. Nonfunctional Key Fob

The key fob is a small plastic controller used in keyless entry systems. This small device contains a short-range radio transmitter that sends a distinct signal to a receiver unit inside your car. When properly functioning, this controller locks or unlocks doors and jumpstarts your car ignition with push-button ease. But when faulty, it would be unable to properly send the signal to the receiver unit inside your vehicle, resulting in your car alarm going off for no apparent reason.

Person Using Key Fob to Turn Off Car Alarm

With car key fobs, their batteries go dead after long periods of use – in which case, a battery replacement should resolve the problem. They also need to be reset from time to time. If you wonder, “Why does my car alarm keep going off in the middle of the night?” and you suspect your key fob is not acting right, take it apart and inspect if there are skewed buttons or broken contacts. If these connections check out, you may need to scan it with a code reader (view on Amazon) or reprogram the controller – either on your own or with the help of a professional.

2. Defective Hood Latch Sensor

Apart from a malfunctioning controller, other sensors in your car may trigger your car alarm to go off randomly. An example of this is your hood latch sensor, which consists of a simple electrical switch that senses when the hood is open or closed. A working hood sensor picks up when your hood latch is open, closes the electrical switch, and illuminates the dash with a warning light. But if the hood sensor is defective, the car alarm would go off instead – it doesn’t matter if it’s late at night or when you are driving.

Several factors contribute to a faulty hood sensor, but the biggest one is dirt. Because the sensor mostly sits in the engine bay above the headlight frame, it is very prone to collecting dirt, debris, and engine grease – causing it to malfunction and trigger a false alarm. Keeping your hood latch and the actual sensor clean not only keeps false car alarms at bay but also protects your vehicle from theft and damage. A good brake cleaner and cleaning brush are all it takes to clean your hood latch sensor. If you still hear the alarm sound after cleaning, your hood sensor may be damaged, or someone may have tampered with it. In any case, replace it right away.

In this video by Youtuber Hazy, the presenter explains how a hood latch triggers a false signal that sets off your car alarm and shows how you can replace the hood latch on a Range Rover Sport & LR3:

3. Poor Hood Latch Connection

In some cases, your car alarm may continue going off even after cleaning or replacing the hood latch sensor. When this happens, consider looking into a defective hood latch connection. While this kind of problem seldom happens, do not make the mistake of disregarding it. When a hood latch is faulty, it can trigger false alarms and adversely affect your car’s control unit, leading to incorrect commands and reading, such as turning the airbag light on even when there isn’t any problem with the airbag function. 

If there are no signs of damage, disconnecting and reconnecting the hood latch connection usually makes it work. Otherwise, you would need to inspect your hood latch connection for any of the following – cable fraying or binding, setting of rubber stops on the hood, condition of the pull handle assembly, and wear, misalignment, or damage of the actual latch. Check if the levers or springs are worn-out or bent. Depending on your findings, be prepared to spend at least $240, including labor.

4. Faulty Door Lock Sensor

The door lock sensor is another thing that can cause your car alarm to go off. This sensor usually has two wires to it – an open and closed circuit – and is generally installed inside the door lock actuator. Because of its setup, the door lock sensor is typically expected to act up during rainy weather when water can seep through the door lock actuator connector. Its internal wirings also eventually fail as a result of normal operation. For specific vehicle makes and models, the release cable bracket on the actuator is prone to breakage.

Sealing the connector with protective grease and identifying the water leak source helps fix the issue. Inspecting if the door lock actuator works via key fob or door switches and watching out for accompanying buzzing or humming sounds when hitting the switch also help narrow down the problem. In the case of faulty wiring, a scan tool helps determine which vehicle door has caused your vehicle alarm to keep going off the most. Whichever door comes up, it is a must to inspect the door lock connector and actuator – to see if any of these parts require replacement.

This video covers this problem with other common issues in his 3-minute video. He also demonstrates a quick way to fix the random car alarm problem, which is proven to work on Honda Acuras and BMWs:

5. Low Battery Level

Your car alarm randomly going off in the middle of the night and finding your car battery dead the next morning are sure indicators that something is wrong with your car battery. Not only is the battery bad, but it is also the main culprit behind your pesky anti-theft alarm. Probably unknown to some vehicle owners, one of the main functions of a car alarm is to warn the driver about low battery levels. Hence, turning the engine on with a dying battery will instantly set your car alarm off.

So, the next time your car wails when you turn on the engine, do not panic. Get your voltmeter out and check its running voltage. If the reading shows less than 12.6V (or whatever your owner’s manual specifies), then you may need to either jolt your battery or have it entirely replaced.

6. Corroded or Rusted Battery Terminals

A low battery level is one thing that sets your car alarm off, while corroded battery terminals are another. In this second scenario, the battery is not necessarily running low. But because of the rust forming on the terminals, the battery cannot give off enough power to different car parts. Your vehicle’s alarm system then interprets this as a low-battery condition and consequently sets off the alarm to give you a warning.

Apart from moisture and salt, improperly charging your car battery can lead to rusting or corrosion. When a battery is undercharged, corrosion forms on the negative battery terminal. Conversely, an overcharged battery will have rust visible on the positive battery terminal. You can clean corroded battery posts and terminals using a commercial-grade battery cleaning agent and a wire brush, as long as there is only minor corrosion. But if both battery terminals are severely rusted (with corrosion eating away at the metal), I suggest replacing the entire battery.

7. Weak or Overly Sensitive Sensor Connection

Different cars have different shock and movement sensor types. Older cars, for instance, normally have only two types of sensors – a door and a shock sensor. Whereas more recent vehicles would have more. Older sensor types would have fixed settings, while newer ones may be adjustable. Similarly, sensor sensitivity depends on having either a factory or an aftermarket alarm system. Perfect examples of how sensor sensitivity varies are Audi and Volkswagen automobiles, which are known to have over-sensitive sensors from the factory.

Regardless of the number or sensitivity of your vehicle’s sensors, what remains unchanged is that they are linked together. Door sensors, shock sensors, microphone sensors, proximity sensors, glass-break sensors, and tilt sensors – even if only one of these gets triggered, your car alarm will surely go off. Because these sensors feed off the main battery, it is crucial to check if there is a solid electrical connection across all of them. If you are uncertain about what to look for, take your car to a local auto shop to have your vehicle’s car alarm professionally inspected.

8. Disconnected Circuitry or Wiring Problems

Somewhat related to overly sensitive sensors, wiring is another thing you need to look into when your car alarm keeps going off. Sometimes, it is not your battery, sensors, or key fob that is at fault. Instead, a part of your electrical wiring that links to these components may be faulty or disconnected.

A sure-fire way to determine if this is your problem is to look for accompanying symptoms. If your headlights flash or your horns blare alongside the non-stop screams of your car alarm, you may be dealing with wiring problems. Otherwise, the trigger for your car alarm may be coming from somewhere else.

9. Problematic Control Module

ECUs or Electronic Control Units are becoming increasingly complicated with newer vehicle models. They are designed to process tons of information and mechanical operations and are often integrated with the car alarm control unit. If the ECU develops a problem, it can send false signals to different components, misleading the car alarm system into thinking that the vehicle’s security has been compromised. If this goes undetected, it may lead to those bothersome instances where your car alarm keeps going off randomly.

From all the items listed, this is the one thing that you cannot diagnose on your own. Take your vehicle to an automotive specialist, as that person would have the proper tools to deal with this issue. If this is what’s setting your alarm off, your ECU will ultimately need reprogramming.

10. Poorly Installed Alarm System

Factory alarm systems only provide a basic level of security and anti-theft protection to some extent. This limited layer of protection is the main reason most vehicle owners opt for an aftermarket car security solution. The downside, however, is that aftermarket car alarms are often improperly installed, especially if done inside a home garage. One of the tell-tale signs of an incorrectly installed vehicle security system is if your car alarm keeps going off at night.

If you installed the car alarm system on your own, double-check the instructions in the installation manual to make sure you have done everything to the T. But if a professional mechanic did the job, go back to that auto shop and explain your dilemma. Usually, a proper reinstallation of the alarm system will eliminate your vehicle’s random wailing episodes at night.

How to Turn off Car Alarm

Turning the Car Engine On

On top of the fixes discussed in the previous section, here are other ways on how you can turn off the incessant wailing of your vehicle:

Turn Your Car On

In some cases, your screaming car will allow you to turn the ignition on. Go ahead if you can, as doing so may stop the car alarm from continuously disturbing the whole neighborhood. If this doesn’t work, try turning the key to the ACC position (where you can play the radio without the engine running). It may take a few minutes – and lots of patience – before it works.

Lock or Unlock Your Car Doors

Using the lock/unlock buttons on the key fob can, at times, remotely stop the alarm. Otherwise, use the physical key tucked inside the plastic controller to lock and unlock the car doors.

Look For the Shut-off Switch

Select aftermarket alarm systems have a switch concealed near the driver’s feet that can shut off or disable the car alarm. Refer to your alarm system’s instruction manual to see if your car alarm has this feature. If a professional mechanic took care of your car alarm installation, you should have already been told this information.

Remove the Alarm Fuse

If options like fumbling with the key fob and locking the doors do not work, removing the correct fuse from the fuse box will do the trick. Just make sure to first detach the battery terminals before pulling the fuse, so you don’t get electrocuted. Understand that this option is applicable only for older cars, as modern ones have their alarms integrated into the vehicle’s central electronic module.

Pull the Wires

If you installed your car alarm system and are mechanically inclined, you may be able to perform this by yourself (or with the help of a friend). Even if most aftermarket car alarms have their wires placed under the steering wheel, I would not recommend this step unless you have full knowledge of your car alarm system.

Reset Your Car Alarm System

Especially for vehicle security systems that come with their own alarm control units, it is possible to reset the alarm system if your car alarm keeps going off at night. Check the manual to know how it is done.

Completely Remove Your Car Alarm System

If all else fails, your last resort is to deactivate the entire system – at least for older cars. You may do this both ways – partially removing the car alarm by snipping the wires or removing the unit and wiring from your vehicle entirely. A partial removal allows you to reconnect the car alarm system in the future. A complete removal, on the other hand, means there is no turning back. For newer vehicles, disabling your car alarm system will also necessitate software manipulation.

Watch this video by Lessco Electronics for tips on how to properly remove your car alarm system:

There are different ways that you can go about shutting off your car alarm. You may even need needle nose pliers (or a fuse-pulling tool) apart from your trusty owner’s manual. What is important is addressing the problem as soon as possible to avoid becoming a nuisance to yourself and others.

Conclusion – Why Your Car Alarm Goes Off

In summary, here are the top 10 reasons why your car alarm keeps going off at night:

  1. Nonfunctional key fob
  2. Defective hood latch sensor
  3. Poor hood latch connection
  4. Faulty door lock sensor
  5. Low battery level
  6. Corroded or rusted battery terminals
  7. Weak or overly sensitive sensor connection
  8. Disconnected circuitry or wiring problems
  9. Problematic control module
  10. Poorly installed alarm system

The next time you wonder, “Why does my car alarm keep going off in the middle of the night?” you should be able to resolve the problem without a hassle. Not only will the information in this guide save you from fines and embarrassment, but it will also ensure that your car alarm system is properly functioning – apart from guaranteeing you and your neighbors a good night’s sleep.

Kris Peter

Adventure seeker and off-road enthusiast. I love the thrill of going off-road and taking on the elements.

Recent Posts