Car alarms are an important safety feature to deter and stop car theft. However, a car alarm that is triggered for no apparent reason can be frustrating, especially at night. So what are the most common causes of random car alarms?
Your car alarm may randomly go off at night if the car battery is dead, the sensors are too sensitive, there is a wiring problem or a problem with the key fob. If you installed an after-market alarm system, you may need to completely reinstall it.
Let’s take a look at the most common reasons your car alarm may be going off randomly at night.
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1. The Car Battery Is Dead
A car alarm may go off to signal that the battery in your car is dead or dying. The battery is the best place to start when you are looking for the cause of a faulty alarm because it is easy and fast to test. If the alarm was going off overnight to signal a battery issue, your car will likely not start in the morning.
Try and identify if there is a reason your battery may have died. Leaving the lights on or the radio running overnight means there is likely not a serious problem with the car, and charging the battery should be sufficient. While newer cars may automatically turn off interior lights and entertainment systems when the car is off, older cars do not have this feature.
If your car battery is dead, you can use another car to jump-start the battery. This may resolve the alarm problem completely, in which case you are good to go!
However, if you are unable to get the battery recharged or the problem repeats the next night, there may be a more serious issue with the battery.
- Car batteries do not last forever. If your battery is old, you may need to have it replaced.
- If there is a white or yellow chalky substance on your battery, it is corroded. You can use baking soda to help remove corrosion, but this should be done with extreme caution to avoid damaging the battery.
- A faulty battery may be a response to extreme temperatures. Older batteries may have trouble starting in extremely cold or hot weather. If your battery is sensitive to temperature, it is best to keep it in a covered area such as a garage. However, this is often a sign of a weak battery that may be on its last leg.
2. The Sensors Are Too Sensitive
The car alarm uses sensors to determine if the car is being broken into. While older cars are equipped with latch and shock sensors, newer cars have many different types of sensors. While you want the sensors to be effective, if they are too sensitive they will give off false alarms.
Cars may include some, but not necessarily all of the following sensors:
- A latch sensor detects the opening of doors, the hood, and the trunk, typically through a switch or electrical current.
- A pressure sensor is the air pressure inside of the car changes, it signals that a door or window has been opened, and will trigger an alarm.
- A microphone sensor is programmed to sound the car alarm if it hears the sound of breaking glass.
- A tilt sensor detects a change in the angle of the car. This triggers an alarm if the car is placed on a jack or tow truck.
- A shock sensor is triggered when the car is bumped into. Generally, an alarm will only sound for heavier hits, but things like a small animal or acorn could trigger a highly sensitive sensor.
When the sensors are overly sensitive, the smallest disturbances around the vehicle can cause the alarm to sound.
Older cars often do not have variable sensor sensitivity, so they cannot always be changed. Newer cars typically allow you to fine-tune the alarm sensitivity.
You will need to purchase a diagnostic scanner that plugs into the car on the driver’s side dash in order to adjust the alarm. The scanner can be used to reprogram the sensitivity settings. Diagnostic scanners are often less expensive than taking the car to a professional, but if you are not comfortable, an auto shop can also fix this for you.
If you installed the alarm after purchasing the car, consult the alarm manual for instructions on adjusting the sensitivity. When you are purchasing an after-market alarm, you should look for one that allows fine-tuning.
3. A Latch Sensor Is Blocked
Latch sensors in your doors, hood, and trunk communicate with one another via a switch or electrical signal that indicates when they are next to one another. When the pieces become separated, the car registers them as open, which can set off the car alarm.
If the alarm is going off when these latches are closed, it could be that a sensor is blocked. Dirt, grease, and oil can all build up on the sensor and prevent it from registering the hinge as closed.
This happens most often to the hood latch since it is the most exposed, but the doors and trunk can also become blocked.
Luckily, there is a simple fix for blocked sensors. You will need to clean off the sensors with a soap that can handle grease, such as dish soap. If there is any rust around the sensors, you should carefully apply a mixture of water and baking soda.
The hood sensor will be front and center when you open your hood. It is right next to the latching mechanism you depress to raise the hood. Similarly, the trunk latch will be in the middle of the car where you open it.
The door latch is not always accessible. If your door latch sensor is circuit-based, there will be no visible sensor to clean. Sensor locations vary by car, but you should look for a button that runs along the door or frame. Be sure to check for debris on the opposite side that could be depressing the button.
4. There is a Wiring Problem
The car alarm is regulated by an electrical control unit in the dash. The unit is connected to the sensors through wiring, through which it sends signals to communicate whether the sensor is on or off. If there is an interruption in the signal or a weak signal, the control unit can register a tripped sensor.
Wiring problems can be quite complex. Since the wiring is not accessible from outside the vehicle, this is not an issue that you can fix on your own. If you suspect a wiring malfunction, take the car to a professional to identify the source of the problem and explain the options.
5. Your Key Fob Is Malfunctioning
Many key fobs have a panic button that triggers the car alarm to offer a distraction in dangerous situations. Like any electrical component, your key fob can malfunction and send an alarm signal to your car in error, setting off the alarm.
To test whether the key fob is the cause of the alarm, remove the batteries in the fob overnight or for several days, depending on how often the problem occurs. If the alarm does not sound without the batteries, the fob is probably the culprit.
The first thing you want to do is change the batteries in the key fob. Low batteries are a common cause of fob malfunction. Generally, electronic key fobs need battery replacements every one to two years. Keeping up with replacing the batteries can help avoid issues.
If changing the batteries does not resolve the issue, it is often possible to reset the key fob.
This process is unique to each car, so you will need to consult the manual for instructions. It will often involve holding down other buttons on the fob for a certain amount of time.
6. The Alarm Was Incorrectly Installed
Although cars come from the manufacturer with alarm systems, some people choose to install additional after-market alarms. If you installed a new alarm system shortly before the alarm began going off randomly, that is likely the cause.
Although these after-market alarms can be faulty, most often the issue is improper installation.
If your alarm was installed incorrectly, it is best to uninstall the system completely and start again.
Although self-installation can help save money, some systems are too complex for people with no experience. You may need to take the car to a professional who has experience installing alarms to get the job done right.
In Summary
Car alarms are susceptible to occasional malfunctions just like any other device. A car alarm randomly going off at night is typically a sign of a problem with the alarm system.
If your alarm is going off at night, it may be due to:
- Dead car battery
- Overly sensitive sensors
- Blocked latch sensor
- Wiring problem
- Malfunctioning key fob
- Incorrectly installed after-market alarm
Using the tips in this article will allow you to resolve the problem yourself, although you can always take your car to a professional if you are unsure.