Why didn't my car alarm go off?

Why Did Not My Car Alarm Go off When Window is Broken

Have you ever experienced a break-in but found that your car alarm didn’t go off when the window was broken? As someone who has experienced this first hand, I researched and discovered several reasons why a car alarm might not go off when the window is broken.

Why your car alarm didn’t go off when your window was broken? Reasons range from the windows not being connected to the security system to a defective key fob, problems with the car battery or wiring, broken sensors, blown fuses, or no alarm in the security system.

In this article, I will share my findings and provide you with a better understanding of what could have gone wrong with your car alarm system.

By referring to this table, you can get a slight idea about possible reasons and solutions.  

                  Reason                                    Solution
Windows are not connected to the security system    Upgrade to a newer security system
  Problem with the car battery    Replace the battery or try recharging the battery manually  
  Battery terminals are rusted or corroded  Clean the terminals
  Problems associated with car wiring    You should ask for a mechanic
  Defective key fob    Replace the key fob
  Sensors are broken    Need to be replaced
  Blown fuse  Check and replace with a new one
  No alarm in the security system  Buy and install a car alarm

So, buckle up, and let’s dive in!

No Connection between Windows and the Security System

Generally, if you own a car with an old security system, you have to open the door of the car to go off the alarm because they usually have a door sensor only. To get an alarm to go off in an attack on the window, your car security system should have special sensors such as shock sensors, microphone sensors, tilt sensors, and proximity sensors.

At least the security system should have a shock sensor to detect the shock when smashing the window or a microphone sensor to identify the cracking sound.

So, to get notified when a thief cracks your car window, you have to upgrade your car security system to a new one with more features.

Insufficiently Charged car Battery

car battery

If the battery doesn’t work properly or the battery charge had been reduced, the car alarm will not work, as most car alarms use power from the battery. This happens if there is an old battery in your car or if you use the car rarely.

To prevent this, you can either install a backup battery in the security system or make sure the battery is always charged sufficiently.

Corroded Battery Terminals

If the battery terminals are rusted or corroded, the alarm and the sensors will not receive enough power to work properly.

You should clean the terminals if they are corroded or rusted and check them regularly to ensure they are clean.

Check out this video to learn how to clean the terminals of the battery.

Why battery terminals are being corroded?

The hydrogen gas released by the sulfuric acid inside the battery contributes to battery corrosion. A corrosive environment starts to be created as a result of the gasses’ reactions to the surrounding atmosphere. Additional components like salts and moisture quicken the process.

Wiring Problems

Car alarms go off after receiving signals from the sensors. If there is no connection between the sensors and the alarm, it will not work at all.

It can be easily and quickly fixed by a professional.

Defective Key Fob

Key fob

Sometimes, when the key fob is broken, the security system might always feel like it shares signals with the key fob. Then the security system thinks there is no thief, it is you.

First, check the key fob battery and replace it. If it does not solve the issue, check for damaged contacts or crooked buttons by disassembling the key fob. You can reprogram your remote control yourself or hire a professional to do it. If necessary, replace your remote.

How long do the batteries in the key fob last?

If you are using the key fob moderately, they usually last 3–5 years.

Errors with Sensors

Usually, a car security system’s lifespan is 4 to 5 years. After that, you have to replace the security system. If the sensors malfunction, the alarm will not receive any signal when a thief breaks into your car.

If you are using an old one, you have to check the sensors and security system regularly to ensure it is working properly, as sensors stop working as they get older.

Blown Fuse

If the fuse of the security system is broken, it will not receive any power. So, you have to check the fuse box (fuse box is usually located at bottom of your dashboard near steering wheel) and replace the fuse with another one with the same size, type, rating, and amperage.

 How do I identify a broken fuse?

The metal piece inside the fuse is melted or broken, and the fuse may be discolored and cloudy.

This video explains you how to identify a blown fuse.

There is No Alarm in the Security System

This usually happens if you have bought a used car. If there were a problem with the car alarm previous owner might remove it.

So, check whether your car security system has an alarm, and if there isn’t one, you’ll have to buy and install one.


 How do I reset my car alarm?

Remove the negative terminal of the battery and reconnect it after a minute. By disconnecting the battery, it will silence the siren and reset the alarm.

What sets off car alarms?

Modern automobiles are equipped with several alarm systems that are wired to sound on their own whenever they spot signs of an intrusion, like a picked lock, a broken window, or even a bumped windshield.

How do thieves smash car windows?

The thief or thieves typically engage in this activity while walking or cycling past cars and peering inside to see if anything of value is readily apparent. Then, when the chance appears to be right for them, they will simply smash your car’s window and take what they want.

How can car thieves be deterred?

Install a theft deterrent and an audible alarm system. Visible deterrents may also be effective, such as a steering wheel lock, window etching, or the flashing light of an alarm system.


Hope I helped you with the details on why the car alarm did not go off when window is broken. Now you know what are possible causes and solutions to those problems.

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