Car Alarm Goes Off When Unlocking With Key

The incessant going off of a car alarm can be exasperating. The frustration is even more when the alarm is up against you, the car owner. It makes it seem like you are some random car thief trying to unlock a vehicle that isn’t yours when all you intend to do is to get in your vehicle with its key. 

Now you’ve got questions on why this happens. Why would your car alarm make such noise when you try opening your vehicle with a key? What other reasons make a car alarm needlessly scream and what is the possible solution to this. Let’s take this one at a time. 

Why Does Car Alarm Goes Off When Unlocking With a Key?

First, it’s a sign that your car alarm is functional. The trigger is because your car can not tell what opened its door since it is not its key fob. It is not sure if it is the key or its lock is being picked so it does what it should do which is to alert its owner that an uncoded entering is happening.

The key fob of every vehicle is coded for that vehicle. When it is used for opening its door the vehicle recognizes its code and disables its alarm but this can’t apply when you use a key. 

However, the raging alarm that was triggered when you opened the car with a key will be disabled once you put the car key in the ignition to start the vehicle. This is because once the car key is in the ignition the special chip on the car key is recognized by the vehicle and this disables the alarm.

Other Reasons Your Car Alarm Goes Off Besides Attempted Car Theft & Solutions

1. A dull car remote or key fob: 

New model vehicles come with a car remote. The remote serves as a smart key. It has buttons for opening the car door, closing it, and setting off the car alarm, and for some vehicles starting the engine. All these without actual contact with the car. The car remote runs on mini batteries which can go flat or drain out. 

When this happens, the remote may start malfunctioning on its own. It may trigger the alarm when you intend to unlock the vehicle or start its engine or do something outside your intention.

Possible solution

If the incessant car alarm trigger is tied to a malfunctioning key fob, then try changing its batteries. Schedule a visit to a mechanic shop or any tool store to request a key fob battery change. The batteries cost about four to six dollars on average.

When the battery has been replaced observe your vehicle and see if the car alarm problem stops or persists. If it stops then you are good to go, if it persists then the key fob may not have been the problem.

2. Problem with the hood latch: 

Within the hood latch of modern vehicles lies special sensors that alarm the car alarm when unauthorized persons try raising the car hood. This scheme was made to protect the vehicle and its battery from theft. Now, if the sensor on the hood latch was poorly installed maybe a wire wasn’t properly fixed, which will result in a flaw in the hood latch sensor. Thus causing it to unnecessarily trigger the car alarm. In addition to a poor installation, a hood latch sensor stained with oil or dirt can cause the sensor to develop a flaw too. And a flawed sensor may unnecessarily trigger the car alarm.

Possible solution

If the car alarm going off unduly is tied to a malfunctioning hood latch sensor, you should try cleaning the hood latch. You do this by first identifying where the hood latch sensor is on your vehicle then you wipe it with a clean cloth and a brake cleaner. Also, see to it that there is no installation no problems and all wires are well connected. 

3. Problem with the car battery: 

If there is an issue with your car battery it is likely going to reflect in the functioning of the car alarm. Your car alarm may be triggered when you try kicking off your car with a low battery. This trigger is to draw your attention to your battery.

 A rusty and corroded battery is likely to also cause your car alarm to go off unduly too. This is because a battery helps in the proper functioning of a vehicle and a problem with the battery will invariably affect some functions of the vehicle (car alarm inclusive).

Possible solution

If the problem with the car alarm is connected to a low car battery, you should change the battery for a new one. You may first confirm you have a slow car battery by using a voltmeter to determine its charge level. If its voltage reading is below 12.6 that is an indication that your car battery is almost completely drained and you should change it. 

You can get a new one for about fifty to two hundred dollars. If the raging alarm is due to rusty battery terminals then you should get the terminals cleaned. You can always get professional help for that or purchase a battery cleaner and apply as instructed. This should help bring some sanity to the car alarm.

4. Improper alarm installation: 

Another likely reason why a car alarm will needlessly go off is if the car was not well fixed in the first place. If that is the case the car alarm will be receiving undue signals and will respond to them accordingly by going off. A fault with the wire works of the car alarm can be a source of the problem.

Possible solution

The most likely solution to an improper alarm installation is having it properly reinstalled. You can always call the attention of the automobile mechanic who had the job done to take a second look at it.

How to Turn Off a Car Alarm Without a Key Fob

a. Try locking your car doors. If the alarm went off while you tried opening your car door with a key, your car tries sitting in your and has its doors electrically locked. This should help turn off the alarm.

b. If locking your car doors did not work you can try putting your car key in the car ignition. Usually, the car should recognize the chip on the car key if the key is originally for the car. This should help turn off the car alarm.

c. If the first two did not work proceed to start your car engine and leave it running for a while. Usually, this should help put the alarm to rest.

d. Finally, try unplugging the fuse connecting the alarm to the power source. This should completely turn off the alarm. Unplugging the fuse may be challenging if you’ve not done it before. The vehicle owner manual will serve as a better guide on where to find the fuse and how to do this.


A triggered car alarm can be frustrating to deal with. You should identify the cause of the trigger and have it sorted accordingly.