Car Alarm Goes off When Unlocking With Key: Reasons

Car alarm goes off when unlocking with key situation has boggled the minds of numerous new car owners. Several reasons cause the alarm to go off as you unlock the door with a key, and the most common reason is using a key after closing the door with a remote key or fob.

Car Alarm Goes Off When Unlocking With Key

The alarm will also go off in case of a low or damaged battery, faulty remote key, overly sensitive shock sensors, and a faulty microswitch.

Continue reading this complete guide as we go through the reasons why your car alarm goes off and what you can do about it.

Why Does Your Vehicle Alarm Goes off When Unlocking With Key?

Your vehicle alarm goes off when unlocking with a key because of sensitive shock sensors, a faulty microswitch, and a low battery. Opening the door with a key after locking it with a key fob triggers the alarm, as well as a faulty key fob and an activated panic button.

– The Car Was Locked With a Key Fob 

Your car key fob sends encrypted codes to your car door. If you use it to close the door, you must use it to open it if you do not want to trigger the alarm.

If you attempt to use the key, the system does not detect the codes but instead interprets your key as an attempted break-in. You need such a security system for your vehicle.

– The Remote Key Is Faulty

A faulty key fob or remote key will trigger the alarm when you unlock the door. The key should deactivate the alarm system when you unlock the door.

Reasons Why Does Your Vehicle Alarm Go off When Unlocking With Key

However, if the key is broken, the alarm system remains active even after pressing the unlock button. The key will also malfunction if its batteries have low voltage or are damaged.

– The Shock Sensors Are Overly Sensitive 

If your car’s door lock sensor is overly sensitive, any slight movements or vibrations near it will cause the alarm to go off. Sometimes, the alarm will go off when someone passes or runs near the car or a dog barks. Hence, touching the door lock with the key will activate the alarm immediately, even if you use the right car key.

– Low Battery 

Many car owners ask, “Why does my car alarm keep going off in the middle of the night?” A low or faulty car battery will cause the car alarm to go off unexpectedly. You also need to check if the battery terminals are corroded.

The alarm and other systems require a fully charged battery to run properly. Hence, charging the battery may stop the random alarms.

– An Active Panic Button 

The panic button is an emergency security measure that enables you to activate the alarm when a suspicious person approaches your car.

Depending on your car’s make, the panic button on your remote key may be yellow or orange.

The alarm sounds when you press the remote button, including an accidental touch when unlocking the car.

– A Faulty Microswitch 

The microswitch is located behind the lock cylinder and connected to the body control module. The switch alerts the control system when you enter the car to deactivate the alarm system.

A damaged microswitch causes the alarm to go off when you open the door with a key.

– Faulty Hood Latch Sensor 

The hood sensor safeguards your car from theft of the engine compartment components. The switch stays open as long as the hood is closed. If the hood is open, the switch closes and sends a warning on the dashboard.

Faulty Car Hood Latch Sensor

If the hood latch sensor is defective, the car’s alarm will sound as you open the door or drive. A faulty latch sensor will not warn you when the hood is open.

– Faulty Electrical Wiring 

The components of the alarm system may be working properly, including the key fob, sensors, and battery. However, the wiring connecting all the parts may be faulty.

If the wiring is the problem, the headlights and horn will go off whenever your car alarm goes off unexpectedly.

– Poor Installation

Most car models come with a basic alarm system. The factory system does not guarantee top-level security, creating a need to install aftermarket solutions. The aftermarket solutions offer better anti-vandalism protection when installed properly.

A common problem with aftermarket car alarms is poor installation, which causes sudden alarm triggers. If you installed a top-quality alarm system, it should have a user manual. Check the instructions again to identify any installation errors, or ask the car shop to check them.

– Problems With the Control Module 

If you are asking “Why does my car alarm go off randomly? You need to check your car’s control unit. The control module processes different operations, including the alarm system.

A defective control module may send a false signal of vandalism and cause the alarm to go off. You need professional help to detect and fix issues with the control module.

How To Fix Your Car Alarm That Goes off When Unlocking With a Key?

To fix your car alarm that goes off when unlocking with a key, check the defective part of the alarm system. If you lock the door with the key fob, use the same to open it. It helps if you consistently use the same locking method.

Reconfiguring the shock sensors and replacing the battery may also fix the problem.

– Fix the Key Fob 

The problem with the car alarm going off even when unlocked can persist until you fix the faulty key fob. You can tell the remote key is problematic if the alarm system stays on after unlocking the car.

Fixing Car Alarm That Goes off When Unlocking With a Key

Start with replacing the batteries and testing their functionality. A reset is necessary if the problem persists with new batteries.

– Reconfigure the Sensitive Sensors 

Over-sensitive sensors are annoying but easy to fix. The car owner’s manual guidelines are enough to help you adjust the settings and make the shock sensors less sensitive.

Consider installing new sensors that are less sensitive if adjusting the original sensors does not fix the issue.

– Charge or Replace the Car Battery

Charging the car battery will restore the normal functions of the alarm system . However, a replacement is preferable if the car battery keeps draining or has rusted terminals.

Use a voltmeter to test if the battery has enough voltage. Remove the corrosion with a battery cleaner and test the alarm system again to see if the battery is charged but has corroded terminals.

– Reinstall and Reset the Alarm System

The unexpected alarm sounds will persist if your alarm system is faulty or improperly installed. Consider replacing an outdated or low-quality system.

However, if you have a good alarm system, reinstalling and resetting it may eliminate unwanted warnings. In addition, consider replacing rusty wiring while reinstalling the system.

– Seek Professional Help

You can change batteries and reset a sensitive sensor without professional help. However, you need a mechanic to fix a broken microswitch and alarm fuse.

After fixing the issues mentioned, you will also need professional help if the alarm system malfunctions.


1. Does a Low Battery Make the Car Alarm Go Off? 

Yes, a low battery can make the car alarm go off. The car alarm warns you when someone tampers with your parked car. The alarm also warns you when the battery is low. Hence, the alarm goes off automatically in case of a low or dead battery.

2. Is Your Car Alarm Draining the Battery?

Yes, your car alarm can drain the battery in standby mode when activated. It drains more power when triggered than on standby mode. However, take note that it takes several weeks for the alarm to drain all the power in your battery.

3. How Can You Use the Key Fob To Stop the Alarm From Going Off?

You can use the key fob to stop the alarm from going off by pressing the panic button twice. The remote key should be within the car’s range. The panic button is often orange or red, marked with a horn.

4. How Can You Turn off the Car Alarm?

You can turn off the car alarm by pressing the key fob, locking the car doors, or disabling it with the switch-off button. Alternatively, disconnect the wiring, reset it from the control unit, or remove the alarm fuse. Any of these methods will turn off the alarm on your car.

Conclusion of My Car Alarm Go off When Unlocking With Key

Why Does My Car Alarm Go Off When I Try to Unlock It with the Key?

When experiencing car door unlocking causes and fixes, it’s essential to understand why your car alarm may go off while trying to unlock it with the key. This issue can stem from various factors, such as a faulty alarm system, disrupted wiring connections, or a key fob malfunction. Consulting a professional automotive technician can help identify the root cause and provide the appropriate fixes to rectify the situation.


A car alarm that goes off when unlocking the door is disturbing.

We have discussed the causes and fixes of this problem, and here are the main lessons:

  • Unlocking the car door with the key after locking it with the key fob triggers the alarm.
  • Defective parts, low battery, bad terminals, and a poorly installed alarm system cause sudden alarm signals.
  • Resetting the alarm and replacing the faulty parts stops the sudden alarms.
  • You can turn off the car alarm with a key fob or switch-off button or disconnect the wiring.
  • It takes several weeks for the alarm to drain your battery.

The next time your alarm goes off suddenly, remember that you can switch it off and inspect the alarm systems for dysfunctional components.

5/5 - (14 votes)
Ran When Parked