Car Alarm Keeps Going Off Randomly? (Here’s How to Fix it)

Having a car alarm that keeps going off suddenly in the middle of the night will most likely not be liked by either your neighbors or you. Here is what causes it and how you can fix it.

Car Alarm Keeps Going Off Randomly

The car alarm buzzing for no reason is a common issue reported by many people. The problem gets even more frustrating at night when people are sleeping, and suddenly your car alarm goes off for no apparent reason.

Why does this happen? Luckily the alarm is not getting off every time because of a thief; sometimes, a faulty installation or other reasons also cause the alarm to go off.

In this article, we look at the causes of why your car alarm keeps going off. We will also talk about what to do about it and take a look at some related questions.

7 Causes Why Your Car Alarm Keeps Going Off Randomly

The most common reason why a car alarm keeps going off randomly is low battery voltage or an incorrectly set movement sensor. It can also be caused by a faulty hood latch sensor, door lock sensor, faulty key fob, or an incorrectly installed car alarm.

Here is a more detailed list of the causes why a car alarm keeps going off randomly:

1. Low Battery Charge or a Dead Car Battery

Car Battery Charger

A bad car battery or low battery charge is a widespread problem for a car alarm that goes off at night. If you hear the car alarm going off at night and the car battery is dead in the morning, the car battery may be bad.

If your car alarm is going off, but you can still start your car without issue, it is most likely something else faulty.

You can test your car battery with a car battery tester or just by using a multimeter to see how good it is and replace it if it is bad.

2. Sensitive Shock/Movement Sensor

Car Alarm System

A sensitive shock or movement sensor triggers the alarm even if a dog or a cat gently touches your car. The type of shock and movement sensors you have in your car depends greatly on your car model and if the car alarm is an aftermarket alarm system installed in your car or a car alarm from the factory.

In some car models with a car alarm from the factory, you can program the shock and movement sensors’ sensitiveness with a diagnostic scanner.

This is often needed on cars like Audi and Volkswagen because their sensors are over-sensitive from the factory and will go off sometimes.

Some aftermarket car alarm systems do also have adjustable sensors. Check the car alarm manual for more information.

3. Faulty Hood Latch Sensor

Latch Sensor Location

Modern vehicles have a hood latch sensor, which triggers the alarm if someone tries to force open your car’s hood.

Depending on your car’s condition, very likely dust, grime, and debris will collect where the hood latch sensor is located, and this causes the alarm to go off.

To fix this problem, locate the sensor and have it cleaned. If you can still hear the alarm sound, maybe someone tried to tamper with the sensor, or the sensor is damaged. Replace the sensor if you think it may be faulty.

You can find the hood latch sensor inside the hood lock most of the time, but it can also be installed externally.

4. Faulty Door Lock Sensor

Door Lock Sensor

The same as with the hood latch sensor, your car alarm monitors your car doors to make sure no one is opening your door.

Therefore a faulty door latch sensor can cause the car alarm to go off. The door latch sensor is often installed inside the door lock actuator but can sometimes be installed externally from the lock.

To find the faulty door latch sensor can be tricky if it just happens sometimes, though.

A door latch sensor usually has two wires to it, which are an open circuit when the door is open or closed circuit when the door is closed or vice versa. This makes it easy to measure with a multimeter.

The door actuators are often located inside the door, though, so it might be a little bit difficult to measure if you do not measure from the control unit instead.

5. Faulty Key Fob

Key Transponder

The key fob, also known as a car remote key, is a device used to lock/unlock your car doors and even start the engine with just a button push.

Since the key fob also has controls linked with the car alarm system, a malfunctioning or faulty key fob can send an incorrect signal, which may trigger the car’s alarm.

You can check and replace the essential key fob batteries or reset the device to fix the problem. When you have replaced the batteries and you have communication problems, you may have to reprogram your key fobs in some situations.

6. Incorrect Installation of the Alarm

Car Installation Alarm

If you have recently installed a new car alarm system and noticed that the alarm keeps going off for no reason, it may be because of incorrect installation.

If you let a mechanic workshop install it, go back and explain your problem, and if you installed it by yourself, it is time to recheck the installation manual and double-check everything.

7. Bad Alarm Control Module

Alarm Control Units

Car alarms installed from the factory often have an integrated alarm control unit and a main electric component control unit, so a faulty control module is not common.

An aftermarket car alarm often has an alarm control module that controls all sensors and switches; if this control module fails, it may cause the car alarm to go off now and then.

What to do if your car alarm keeps going off

While trying to diagnose a car that keeps going off can be quite tricky, without the right tools, there are still some things you can try to see if you can fix it by yourself. While some of them require some special tools, you can follow the procedure here:

1. Charge the battery & Check the charging voltage

The first thing you need to do is to check the voltage in your battery with a multimeter. It should read somewhere around 12 to 12.5 volts when the ignition is on. If it’s under 12 volts, it is definitely time to recharge the car battery with a battery charger. Charge it fully for 24 hours to ensure it’s fully loaded and see if the car alarm keeps going off anyway.

A car battery should not discharge if you drive it every day if the alternator is doing its job correctly. Start the engine, let it run, and recheck the battery voltage with a multimeter at idle. It should not read between 13.5 to 14.5 volts on idle if everything is correct. If it’s not – you may have a bad alternator which is causing the car battery to drain.

If the voltage keeps dropping under 12 volts at ignition, even if the alternator is charging, you may have a bad car battery that needs to get replaced.

2. Check for any trouble codes with an OBD2 scanner

If everything seems fine with the charging voltage and the car battery, it is time to look for any trouble codes with a scan tool. You can either get one yourself or lend it from a friend or let a workshop check the trouble codes for you. A cheap scanner will not be enough to check for any trouble codes related to the car alarm because most of them can only read trouble codes from the engine control unit.

Also, if you have an aftermarket car alarm, you can’t check for any trouble codes in the car alarm system with a standard scanner. However, if you find any trouble codes, you need to start troubleshooting wherever the codes say the problem is.

3. Lubricate all door hatches & locks

Another easy thing you can try is to lubricate all door locks, the hood and trunk latch with a lubricant to ensure they are correctly closed. If you can reach the connectors, spray some electric cleaner into them is also a good idea. However, they can often be quite challenging to reach without taking the whole car apart.

4. Check the sensitivity setting

If your car has a car alarm installed from the factory, there is a big chance of sensitivity settings for the shock or movement sensor. These settings can most often only be reached with a good scan tool, and the cheaper ones will not handle this task. In some car models, you can reach these settings from your car’s display settings so therefore it’s good to check the owner’s manual for any sign of these settings. If you can find them, you can try to reduce the sensitivity.

5. Change the key fob battery

The last thing you can do yourself is to replace the battery in your key fobs to ensure they are fully charged. While this issue will most often not cause your car alarm to go off, it can happen in some rare cases. Key fob batteries are usually very cheap and relatively easy to replace in most keys. Again – check your owner’s manual for instructions on how to replace the key fob batteries.

If you have tried everything above, but your car alarm still keeps going off, there is not so much more you can do without more profound diagnostic knowledge. Therefore it’s time to use professional help from a workshop with the proper diagnostic tools.

FAQs

Where are car alarm sensors located?

There are door alarm sensors installed inside the lock units of the doors, trunk, and hood of your car. You will also find motion sensors and other types of trigger sensors, depending on the car model and how modern it is.

Will a car alarm go off if the battery is dead?

If the car battery is completely discharged, the car alarm will not work. However, the alarm does not require a lot of power, so if there is just a little power left in the battery, the car alarm will work.

Can you turn off a car alarm permanently?

If your car has an aftermarket car alarm, it’s often quite easy to remove the car alarm if you don’t want it. However, if the car alarm is installed from the factory, it may be difficult to remove it completely, but it depends entirely on the car model

How long will a car alarm go off?

Modern car alarms typically go off in 15-30 second intervals, over a period of 5-20 minutes, depending on the car model. Older car alarms could go on for many hours until the battery was discharged.

Conclusion: Car Alarm Keeps Going Off

The best thing to do when your car alarm keeps going off is to check the battery first. If the battery is good, then you want to make sure all the door locks are working properly. You may also need to recalibrate the motion sensors, which can only be done with a diagnostic tool.

The most common reasons a car alarm keeps going off include:

  • Low Battery Charge or a Dead Car Battery
  • Sensitive Shock/Movement Sensor
  • Faulty Hood Latch Sensor
  • Faulty Door Lock Sensor
  • Faulty Key Fob
  • Incorrect Installation of the Alarm
  • Bad Alarm Control Module

Don’t ignore your car alarm if it goes off frequently, as it could be an indication of a more serious problem. If you feel that you do not have the knowledge to find out what is causing the problem, it may be a good idea to contact a professional. Car alarms can be quite complicated on modern cars, and sometimes it’s better to have a mechanic take a look at it.

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Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.