Why Your Car Alarm Keeps Going Off and How to Stop It


Although a car alarm is designed to deter thieves and vandals, a damaged or malfunctioning system can repeatedly go off without cause, creating a loud distraction and leading to complaints from your neighbors and coworkers. In most cases, this is caused by a bad battery, faulty wiring, or a malfunctioning sensor. Whatever the cause, it’s generally an easy and inexpensive fix.

To troubleshoot a car alarm that keeps going off without cause, start by checking the battery, testing the wiring, and inspecting the sensors. If you cannot locate the problem or if it persists, you may have to reset the entire system or take your vehicle to a professional to have it inspected. 

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As annoying as a faulty car alarm can be, it shouldn’t affect your vehicle’s performance. Be aware, though, that if there’s an issue with your battery, you may notice other electrical problems while driving. To learn more about the problem and how to fix it, continue reading below.

How Does a Car Alarm Work?

Although every car manufacturer uses a unique alarm system, most work in a similar way. A sensor connects to each of the four doors, as well as to the hood and trunk of the vehicle. When a driver locks and leaves their vehicle unattended, it arms the system and if someone tries to enter the vehicle without first disengaging the alarm, the sensors issue a loud honking or beeping noise.

In some cases, the alarm may also be triggered by a break in the car’s glass. This happens with a pressure sensor that attaches to and “monitors” the window. When the window breaks, it activates the pressure sensor, and the alarm sounds.

What Can Cause a Car Alarm to Repeatedly Go Off Without Warning?

As with most car problems, there are several reasons why your car alarm may go off without warning. In most cases, it’s due to a problem with the battery, wiring, or sensors.

If your car alarm repeatedly goes off without cause, the first thing you should check is the battery. Although a dying battery often has enough juice to engage the engine, it usually lacks the power supply to maintain your vehicle’s electrical system. This can lead to widespread electrical problems, including a faulty alarm system.

If your battery is more than three years old, it’s likely time for a replacement. Even if it’s younger than three years, a dying battery can still cause problems. To check the health of your battery, take it to a professional or use a voltmeter. If your battery has fewer than 12 volts, it needs to be replaced.

If the wiring to the alarm system is damaged, it can cause the system to malfunction. This is usually the result of a poor installation job or an accident. To check the wiring, visually inspect it for any signs of damage. If you see any frayed or broken wires, replace them.

The sensors in the car alarm system can also malfunction, causing the system to go off without warning. In most cases, this is due to dirt or debris build-up on the sensors. To clean the sensors, use a microfiber cloth and a brake cleaner to clear away debris. If the problem persists, you may need to replace the sensors entirely.

The Problem Could Be a Faulty Fob Battery

If your car alarm keeps going off and you’ve ruled out all other potential causes, the problem may lie in the battery of your key fob. The key fob is the device that you use to unlock and lock your doors, as well as to engage the alarm. Most key fobs have a small button battery that powers the device. Over time, though, the battery can die, causing the key fob to malfunction.

If your key fob is the problem, you’ll notice that the doors won’t unlock when you press the button. In some cases, you may also notice that the button feels “soft” when you press it.

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To fix the problem, open up the key fob and replace the battery. If you’re unsure of how to do this, consult your car’s owner’s manual or take it to a professional.

Related: How to Program a Key Fob (For All Cars)

How to Fix when a Car Alarm Keeps Going Off

Depending on the cause of the problem, you should be able to fix a faulty car alarm without consulting a mechanic. Start by going through the following steps:

The hood sensor relays information to your vehicle’s control module, indicating whether the hood is open or closed. If the sensor is working properly, you’ll notice a warning light on the dashboard whenever your hood is open. If not, the sensor has failed and it’s likely causing the alarm to go off without cause.

Related: What To Do If Your Car’s Hood Won’t Open?

These sensors are usually made from two wires that create an open and closed circuit in the door lock actuator. Due to the location of the sensors, though, rain can seep into the lock and damage the inner wiring, causing the sensors to fail. If they have failed, you’ll notice a buzzing noise whenever you engage the locks.

Even if your vehicle’s battery can hold a charge, if the terminals are corroded, it can prevent the electrical current from flowing properly and cause your car alarm to go off without warning. To clean the terminals, use a wire brush to remove any corrosion.

If the problem persists, it’s likely that the battery is the root of the problem. Many auto stores and service stations will provide a free battery test. In most cases, you can replace the battery yourself, but if you’re unsure of how to do it, consult someone who can.

The Bottom Line

If your car alarm keeps going off without warning, the problem is likely a dead or dying battery, faulty wiring, or malfunctioning sensors. In most cases, you can fix the problem yourself by checking the battery, testing the wiring, and inspecting the sensors. If the problem persists, you may need to replace the entire alarm system or take your car to a professional for an inspection.

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