A car alarm should be reliable and not prone to false alarms. But if your car alarm is going off randomly then you’ll want to get it fixed pronto as it’s not just annoying you, it’s probably pissing off your neighbours too.
So why does your car alarm keep going off randomly?
The first thing you need to understand is that there is a reason why it is going off, it’s not actually random despite not having an obvious pattern.
I’m going to walk you through the steps to discover why it is going off, and how to fix it. Stay calm, follow a logical process, and try not to pull your hair out!
What is going off? Alarm Horn, Siren, Lights?
Pay attention to your alarm
Before hitting the disarm button on your remote, pay attention and note what the alarm is doing. Are the hazard lights flashing? (park lights if you’re a Yank). Is the horn honking? Is the siren sounding. Make a note of this as it can really help with the diagnostic process.
For example, if the siren is sounding, but the lights are not flashing then it is unlikely that the main alarm has been triggered. The problem is more likely to be the actual siren or possibly a bonnet switch.
Identify your car alarm
If you know which make and model of alarm you have then you can skip this step, if not then you’ll want to identify what sort of alarm you are dealing with.
There are a number of ways to do this, look for branded window stickers and check the vehicle documents to see if there is a user manual. Take photos of the alarm remote, dash LED and siren if possible. These can all be sent to your local car alarm specialist who should be able to help.
Read your user manual - Understand how your alarm works
If you have a user manual then have a read through it and find out what sensors the alarm has and how to isolate them. If you don’t have a user manual then search online and find one. I have a user manual page where you can download all of the alarms that I sell and have previously sold.
Most good alarms have diagnostic codes that will report why the alarm has gone off.
Alarm Fault Codes
The video shows how to read an alarm fault code on a Vodafone Automotive alarm. knowing why the alarm has gone off is makes it much easier to fix. For example, if the fault code is always the boot, then I’d ask if the vehicle had been in a prang, or been repaired at the local panel beaters recently.
Not all makes and models of alarm have user friendly diagnostic codes but it’s still worth reading the manual to see if they do.
What has been done to the car recently?
Knowing the story of what has been done to the vehicle recently can help identify the cause of the false alarm. Often that missing bit of information which I’ve not been told would point me in the right direction to figure out what this issue is.
Common reasons for false alarms
Low Vehicle Battery/Loose Battery
Most electrical devices fail to work correctly if they don’t have a good power supply. Your car alarm is no exception.
If your car battery is old or the vehicle has not been used recently then the battery could be the issue. As could a parasitic draw from poor quality GPS tracker.
Another common issue are loose battery terminals with poor contacts.
If your alarm is going off and you can’t stop it with the remote then it’s probably a battery issue.
Faulty Remotes - Phantom Panic Alarm
Well used remote controls are a common cause of false alarms.
The usual culprit is a collapsed tac switch where the internal spring has failed.
How does a collapsed remote switch trigger the alarm?
There are many remote controls that will activate the panic feature of a car alarm by holding the lock button on the remote for 2 to 3 seconds. If the switch has failed it may be transmitting a panic command.
Pocket Activation
Having the remote in your pocket can also also cause a panic command if the button gets pressed unintentionally.
The humble bonnet switch
So many car alarms are sold with poor quality bonnet switches which will inevitably fail in time.
When these fail they will often cause a false alarm, especially after rain.
Get a good quality bonnet switch
I normally replace the switch to a good quality one. It’s disappointing how many companies here in NZ sell switches which will rust.
Battery Back-up Siren Issues
Anyone who reads the blog on a regular basis will be aware of my opinion on battery back-up sirens that have an over-ride key.
These cheap, low budget sirens are not effective and often cause issues. The AVS S5 Sirens are so bad that they even have a sticker warning that they should be protected against water.
If your siren is sounding without the lights flashing then the siren is probably the cause of your false alarm, especially if it is not waterproof and road spray has reached it.
The only battery back-up sirens I recommend are digital ones with an official IP rating.
Over sensitive alarm sensors
Over sensitive alarm sensors along with poorly located sensors are another common cause for false alarms.
Shock Sensors
From my experience shock sensors can often be problematic as explained here.
Diagnostic fault codes are everything when it comes to trouble shooting
Any alarm sensor can cause the alarm to trigger, so being able to know which zone of the alarm is causing it to sound takes all of the guess work out of the equation.
Over sensitive glass break sensors can get triggered by temperature changing in the vehicle that can cause the trim to expand and contract causing a creaking sound.
Leaving a cell phone in car can trigger a microwave sensor to go off.
It can often be challenging detective work trying to figure out what is happening with the alarm and what the driver has done which you’ve not been told about. This leads nicely into what I refer to as a user interface error.
User interface errors
A user interface error is my term for people who don’t take the time to learn how their car alarm works.
Having a basic understanding of how the alarm functions, and how sensors work can prevent most false alarms. For example, if you have an alarm with ultrasonic sensors, and leave a window open then it should not be a surprise if the alarm triggers.
Part of my job is explaining to the owner how the alarm works and being there for aftersales support. If you are the 2nd owner then feel welcome to contact me and I’ll be happy to run through things with you,
People who dabble!
One of the other classics I come across is the builder who decides to unplug the switch on the drivers door so they can sit in the van and with the radio on without the door open buzzer chiming. This results it the vehicle auto re-locking and the alarm re-arming. This can also result in the keys getting locked inside the van.
Insects
Unwanted guests
Ultrasonic sensors detect movement, so having spider webs in front of them can cause the alarm to go off when the little critter crawls past the sensor. Moths can also fly close enough to the sensors to trigger a false alarm.
Rodents
Nibbled wires
If you love your car then you should be supporting predator free New Zealand.
The last thing you want is a rodent in your car, they can do all sorts of damage to a vehicle and it’s wiring. I know of a couple of cases where these have caused an alarm to go off after chewing the wiring.
The photo is shows a rats nest in a 2007 Hilux which I installed an alarm into. I discovered it on my pre-installation check. Luckily this was a fresh nest and no wires were damaged.
It’s hard to decided which I dislike most, a real rat’s nest or a mess or wires I often find when removing an AVS alarm.
This leads nicely to another cause of false alarms: Poor installation work.
Poor installation work
Cheap Installations
The biggest reason why car alarms have a bad reputation is poor quality installation work. If you are hunting around for the cheapest install then don’t expect a quality installation. That said shit installs can be over-priced too.
Shit Alarm Systems
I tend to find that shit installers recommend shit alarms. If your installer cares about doing a good job then they won’t recommend brands like AVS and Mongoose.
Why? Because they put so many limitations on how effective the install can be. Read the reviews to understand more.
Be kind to your alarm technician
Car alarms are designed to be annoying, people often get upset if they get woken up at 3am so I totally understand that it’s frustrating if one has gone off at a bad time (is there ever a good time?)
Just remember, there is always a reason why the alarm has gone off, so working with your alarm installer is going to get a better outcome then taking out your frustrations on them.
Most modern car alarms are very reliable if they have been installed and set up correctly. It also helps if you look after your vehicle and take preventative action before things fail such as booking in an alarm service.
FAQ about false alarms
How do I temporarily disable my car alarm?
Disarm the alarm, open a door, then close it and lock it manually without using the remote.
Alternatively disarm the alarm then remove the fuse or disconnect the battery.
Will a dead battery cause my alarm to go off?
How much does it cost to fix a car alarm?
If it is under warranty then it should be free, but you’ll need to take it back to your installer.
If it’s not under warranty, expect to pay for replacement parts and a hourly rate. By taking my advice and recording the alarm fault code you can help keep the cost down.
Do you have other questions?
Chuck them in the comment section.
