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Car alarms are there for a reason. We all know that. But if your car is just non-stop screaming at you, day or night, you might begin to wonder whether or not it’s all worth the hassle. As well as being irritating for you, your neighbors will slowly begin to resent the noise as well as everyone else doing their shopping at the same time. Ouch.
Luckily, there are solutions. You don’t have to put up with the constant random screeching of your car alarm for the rest of its life.
In this article, we aim to give you some idea of what might be causing your alarm to be going off all the time and, most importantly, what you can do about it.
How a Car Alarm Works
To first begin to understand how to approach a car alarm and fix it, you should understand the basics of how it works.
Car alarms are always on, technically. The circuit is activated the minute you lock your car and set the alarm. However, they are (or should be, at least) almost always silent.
The alarm system involves several sensors. On older cars, you would expect to find just two sensors. That’s a door sensor to tell if someone is breaking in without unlocking the doors using the key. And a shock sensor, which would cause the alarm to sound in situations such as someone smashing in the windscreen or crashing into your car while it’s parked up. Newer cars, however, will have far more sensors – up to ten, and more.
When just one of these sensors gets activated, the alarm begins to sound. In theory, this deters your potential car thief. Unfortunately, though, the car alarm can go off for many other seemingly random reasons, too.
What Sensors are Involved in the Alarm System?
You’ll find a variety of different sensors in the alarm system. These usually include the following, but there may be more on different cars.
- Door sensors – Door sensors work by creating a closed circuit when the door is closed. When the door gets opened before the alarm system is switched off, this circuit gets broken, which in turn triggers the alarm. These sensors are handy for deterring thieves from picking your lock and accessing the car that way.
- Shock sensors – Like door sensors, you’ll find shock sensors on almost any car with an alarm, regardless of its age. Shock sensors pick up “shock waves” – a term meaning any energy wave moving faster than the speed of sound. If these sensors pick up a “shock,” the alarm will activate.
- Glass break sensors – These sensors are more precise than shock sensors and only activate if the windows’ glass is broken. Having these sensors helps to prevent thieves from gaining access to your car by smashing a window.
- Tilt sensors – When someone comes to steal your car, they don’t necessarily have to break into it. They could simply bring a tow truck, reverse up to your vehicle, load it up, and tow it away. Your car will probably be fitted out with tilt sensors to prevent this. These monitor the angle of the car as it sits, parked up. If this angle changes dramatically, the tilt sensors send a message to the alarm to make it sound.
- Microphone sensors – Microphone sensors are designed to look out for sudden spikes in volume, such as a broken car window. If the area you are in is loud already, this will be taken into account so that the alarm won’t be unnecessarily triggered.
You will find many other sensors, such as proximity sensors, in different types of cars. The sensors mentioned above, though, are the most common. You’ll find these in most different cars available nowadays. Aside from the loudspeaker (or “siren”), these sensors are basically the main parts of the alarm system. In newer cars, these loudspeakers are often set up to make various noises, allowing you to customize the sound of your alarm. So that’s nice.
The ECU takes note of all the readings from your sensors and translates this information into whether or not it should send a signal to the siren (as well as the headlights and the horn, on some cars). The battery is an essential part of this system. As with all electrical circuits, it needs a power source.
The last part of an alarm system is the radio receiver. This is linked up to your key fob and allows you to control the alarm (turn it on or off) wirelessly.
On many cars, the alarm is activated by pressing the “lock” button twice. Pressing the button once locks the doors, pressing it a second time activates the alarm. Some manufacturers make their keys with a specific “alarm” button, but this isn’t as common.
What Could Be Causing My Alarm to Go Off at Random Times?
We have seen what components make up the alarm system in a car: the sensors, the loudspeaker, the ECU, the battery, and the radio receiver, along with the key fob.
We will organize these problems into those categories now, allowing you to explore all potential issues together.
It makes sense that for the alarm to be going off at a random time, the problem probably lies with one of these components or the wiring leading to them (if applicable).
Before exploring some potential mechanical reasons, we would advise you to make sure that it’s not just someone playing a joke on you – an old friend, some local kids, anything like that. If the problem persists and you expect this may be the cause, we recommend setting up CCTV.
Sensors, such as the door sensors or hood sensors, work by activating the alarm when the circuit is broken. In theory, this should be just when the door or hood is opened with the alarm is on. However, it could also set the alarm off if the sensor connection is weak.
This could be due to the sensors getting dirty or knocked. Locate them (you can use the internet, your owner’s manual, or other sources to find them) and visually inspect them all for any kind of damage. The easiest one to access is usually the hood sensor. This sensor can also pick up a lot of dirt from the road as you drive, so this should be your first port of call.
You could also use a multimeter to check if there is a solid electrical connection across these sensors.
If you aren’t sure what you’re looking for, take it to your local auto shop and get a mechanic to look for you.
It’s not likely that a problem with the loudspeaker itself will be causing the alarm to activate, but there could be a problem with the connected circuit. Although this would be a very rare occurrence, a good way to see if this is the problem is to look at the headlights and horn. The headlights usually flash, and the horn blares instead of – or as well as – the loudspeaker’s screeching.
Look to see if these are going off as your alarm is blaring. If they aren’t, your problem might be somewhere around here.
The Electronic Control Unit becomes more and more complicated with each new car. They are designed to cope with more information and processes, and each one is more advanced than the previous one.
If the ECU has developed a problem, it may be sending a false signal to the loudspeaker to tell it that the alarm has been tripped. There’s no real way to diagnose this yourself. You’ll need to take it to a specialist automotive electrician with experience in dealing with this. Your ECU may need reprogramming.
If there’s a problem with the battery – such as it being dead – this may interrupt the alarm system. On some cars, the alarm sounds just to let you know that the battery is dead. It shouldn’t be too difficult to get a new one if your battery is dead. To see if it is, try starting your car or turning on the headlights after you’ve turned off the alarm.
You may also find that rusty terminals on the battery lead to an interrupted alarm circuit. After making sure the ignition is well and truly off, clean the battery terminals from excessive rust and dirt using a baking soda solution and an old toothbrush.
Radio receiver and key fob
Your key may develop a faulty signal which the radio receiver understands as “set off the alarm now, please.” This is often due to a dying battery in your key fob. If this might be the case, replace the key battery, and see if that makes a difference.
If it doesn’t, you may want to get some specialist help.
Unfortunately, as with any electrical system, the problem could lie in some obscure place buried deep in the wiring. This will require special treatment, and so you should take it to an automotive electrician. This problem is perhaps not as likely as a component fault, but it’s certainly a possibility.
Automotive electricians will use testing techniques to determine the exact location of the fault, but you should expect to pay a bit more than usual for their specialist skills.
How to Approach Diagnosing This Problem?
We feel that the best way to work out the problem with your car’s alarm is to make a note, whether mentally or literally, of the times it occurs. From this data, you should be able to see whether it happens at a certain time of day (or night), in a certain location, or another variable like this.
Knowing this may give you an indication of what’s setting the alarm off and, therefore, what the problem is likely to be.
For example, if you park your car on the road outside work and heavy goods vehicles (HGVs) are passing all the time, this may represent an issue with either the microphone sensors or shock sensors. If it usually happens when you’re close to your car, there may be an issue with the radio receiver or key fob.
If you are unable to fix the problem yourself, we would recommend taking your car to your local auto electrician (rather than bog-standard mechanic). This will give you the best chance of getting your car fixed. Having your alarm going off all the time can be extremely frustrating, but as with everything, there will be a legitimate cause. You just need to find it, and everything will be fine.