Car Alarm Goes Off When Unlocking With Key (Why + Fixes)

If you own a car, at one point or another, you’ll have problems with the car alarm going off randomly even if nobody is breaking in. On some occasions, the alarm will go off when you unlock with the key.

However, if you’re unfamiliar with this situation, you may wonder why it happens? If you’d like to find out, keep reading!

Why Does My Car Alarm Go Off When I Unlock it With a Key?

When unlocking with the key, your car alarm goes off, especially if you locked the vehicle with your remote key fob. If you don’t use the same key fob to open the car, the alarm is triggered manually. This can also happen if your shock sensors are overly sensitive, if you have a low battery or a faulty key fob. 

To learn more about why the car alarm goes off when using your key and how to fix it, keep reading for more useful facts and tips!

Why Does My Car Alarm Go Off When I Unlock it With a Key?

Car alarms go off for different reasons, though common for this to happen when you unlock with the key. Nevertheless, there are many reasons why this can happen, some of which are listed below:

1. You Locked the Car With a Key Fob

If your alarm keeps going off, the culprit is most likely your car’s security system. Depending on your car model, you can either lock and unlock the door with either a key fob or a key.

Therefore, if you lock your doors with a key fob, you have to unlock them using the same device, otherwise your vehicle will sound off the alarm. This happens as a security measure because the vehicle’s alarm system assumes that someone is breaking in.

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Your key fob is ideally specifically coded to your vehicle, therefore, it transfers encrypted signals to open the car door. So, if you use the keys to open the door, these signals will not be detected, and the alarm will be triggered.

2. Malfunctioning Key Fob

2. Malfunctioning Key Fob

A faulty key fob can cause your alarm to go off when you least expected it. When you use the key to open the doors, the gadget will send a signal to trigger the alarm, which is why you need to have a key fob that’s properly functioning to avoid these alarm issues.

3. Sensitive Sensors

If you have overly sensitive shock sensors, these sensors may contribute to your alarm going off when unlocking the vehicle. These sensors are responsible for triggering the alarm, therefore, your car will rarely be quiet if they are too sensitive.

Some original and aftermarket alarm systems can sense vibrations or slight movements, causing them to go off when another car passes or a dog barks.

Therefore, if your shock sensors are too sensitive, a simple touch when using a key automatically triggers the alarm.

4. Broken Microswitch

A microswitch is wired to the body control module at the back of every lock cylinder to alert it when you enter the car, which disarms the alarm.

However, if your microswitch is broken, the car alarm will go off each time you open the door with a key. If this keeps happening, you likely have a damaged microswitch that needs to be fixed.

5. Low or Corroded Battery

As a car owner, you might have wondered how long it takes for the battery to discharge.

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If you notice that your alarm goes off each time you unlock with a key, this could be a sign that your car battery is running low or the terminals are corroded.

6. Accidental Alarm

If you accidentally press the key fob in your pocket simultaneously when opening your vehicle with a key, the alarm will go off. On most occasions, this happens because the key fob has a panic button that can trigger the alarm if you trigger it accidentally.

How Do I Stop My Car Alarm Going Off When I Unlock it With a Key?

How Do I Stop My Car Alarm Going Off When I Unlock it With a Key?

Fortunately, if your alarm has become a problem, there are several ways to fix it, such as the following:

1. Adjust Your Sensors

For overly sensitive sensors, you can fix this by adjusting them to become more accommodating. You can find their location by checking the owners’ manual.

However, if configuring doesn’t work, you can buy other aftermarket sensors that are less sensitive.

2. Visit a Professional Mechanic

When the problem is a broken microswitch, it can be quite challenging to fix this on your own.

Therefore, to avoid further damage, take your car to a mechanic or professional technician who can repair the microswitch.

3. Replace Key Fob Batteries

When the key fob is a problem, replace the batteries to have it working properly. As well, you can reset the gadget to restore it to optimal performance.

4. Replace the Car Battery

For a low charge or draining battery, you have to replace it for the alarm system to function properly. To check whether your battery is low, use a voltmeter to measure the voltage, and if the terminals are corroded or rusty, use a battery cleaner to remove these impurities.

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Can the Car Alarm Go Off if it’s Unlocked?

Can the Car Alarm Go Off if it's Unlocked?

Ideally, car alarms shut down when the car doors are unlocked. However, if you close the door and the siren continues sounding, you might have an issue with your battery or key fobs.

If you want to know more, you can also see our posts on Avital car alarm reset, Kia alarm reset, and how much is a car alarm.


If your car alarms go off after unlocking with a key, this could be due to sensitive sensors, low battery, faulty key fob, an accidental alarm trigger, or a broken microswitch. 

To avoid these problems, use a key fob to unlock the doors if you used one to lock the vehicle. You should also adjust your sensors or take your car to the mechanic to replace the batteries.

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