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Car Alarm Goes off When Unlocking with Key? – Here are the Causes and Fixes?

Auto Parts and Accessories · November 12, 2022

Your car alarm going off when you try to unlock it is the worst feeling ever. Not only is this a nuisance to deal with, but it also feels incriminating. The way people start to stare at you when the alarm goes off can make you wish that the earth below opened up and let you sink in. 

So, what are the causes and fixes when the car alarm goes off when unlocking with a key? – Causes and fixes are simple. The causes mostly are minor electrical faults with fixes as easy as replacing a battery. 

The causes for the alarm to go off and their fixes require some explaining. Follow along as we discuss the issues and how you can fix them. 

Car Alarm Goes off When Unlocking with Key Here are the Causes and Fixes

Car Alarm Goes off When Unlocking with Key? – Causes and Fixes 

The reasons a car alarm might go off are simple. But, there still are multiple reasons, all with their unique fixes, that might be the cause for your troubles. Here are the most common causes of the car alarm going off when unlocking with a key: 

Confusion Between Keys and Key Fob 

In cars that use both a physical key and a key fob, the security and alarm systems are easy to confuse. And this confusion then leads to the alarms blaring off. 

If you lock your car with the key fob, it engages the safety system. And from this point onwards, this safety system treats anything and everything that tries to unlock the car as a threat. Even your keys are seen as threats by the safety system as it cannot discern between a key or lock picks.  

Fix:  

The car or the safety systems in this situation are not broken. The alarm going off is just a side-effect of a design. As such, the fix in this situation is for you to be aware. If you locked your car with the key fob beforehand, then you should only use the fob to unlock your car. 

Dead Key Fob 

Dead Key Fob 

You use the battery-powered key fob of your car to activate and deactivate the security systems when unlocking. As such, the fob must be working perfectly to ensure that the systems are off when you go to use the key. But, like any battery-powered device, the fob will eventually run out of charge.  

If the key fob is low on power, the button presses you make to disable the security system or unlock the car don’t register consistently. This results in situations where you might assume that the alarms are off. But in reality, the alarms were active and went off the moment you put in your keys. 

Fix: 

The fix to this particular problem is replacing the batteries. Most key fobs are easy to open and use standard disc batteries. Owners can easily change the battery on their key fob and be good to go. 

Dead Car Battery 

Dead Car Battery

The battery of your car is fully drained or dead is another cause for the alarms to go off.  

The security system in your car needs to be powered to receive and process the signals from your key fob. But with a dead battery, the system might either be turned off or unable to receive and process the signals.  

And when the security system is in this state of low power, it functions poorly. The fact that it is unable to process the signals will result in the alarms staying on and going off. 

Fix: 

Checking and either recharging or replacing your car battery is the only fix you need to bring the systems back online.  

If your battery has corrosion and the terminals are rusty, then you might have to replace it. Otherwise, a top-up on the charge should be enough of a fix. 

Damaged or Defective Key Fob 

Damaged or Defective Key Fob

If your key fob malfunctions, then the alarm going off is inevitable. As we have discussed already, the key fob sends signals to the security systems telling it to deactivate. But a malfunctioning key fob might not send the signals properly and ultimately cause the alarms to ring. 

A damaged or defective key fob can act up in many ways. Sometimes it might not send a signal at all, leaving the alarms on. Other times it can send multiple signals all at once, confusing the security system and causing the alarms to blow. 

Fix:  

If a key fob is defective or damaged badly enough that it malfunctions, then it has to be replaced. Each key fob is uniquely coded to its car. And the only way you can replace your fob is by visiting a dealership that can program the new fob to your car.  

Damaged Sensors 

Damaged Sensors

Sensors are integral to modern security systems. Every car employs sensors like vibration sensors that look for collisions and lock/latch sensors that ensure that all the latches are closed. 

Over time and through daily use, these sensors can wear out. Latch sensors can get caked in dust whilst vibration sensors can develop electrical faults and start to send false signals.  

The latch sensors especially cause trouble, as a false read from these while unlocking and opening a door will cause the alarms to go off. 

Fix:  

Sensors that are open to the elements and get covered in dirt and debris often only need to be cleaned. Good dusting is all you need to do, and the sensor will regain proper functionality. 

However, if the damage to a sensor is electrical, it will have to be replaced. 

Filed Under: Auto Parts and Accessories

Mihailo Savic

First and foremost, I am a mechanical engineer. I graduated from the University of Waterloo in 2018 with a degree in Mechanical Engineering.
I have also gained experience in various industries such as aerospace, construction, oil & gas, etc, through my work with different companies.
Also working in the field of pressure equipment (vessels, pipelines and steam generators), such as inspection and testing.

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