Shock Sensors: The Biggest Culprit Behind False Car Alarms
We’ve all been there. You’re at home, or walking down the street, when a car alarm suddenly erupts for no reason. Annoying, right? But here’s the real question: how many times have you actually gone outside to check if it’s a genuine break-in?
Chances are, you didn’t find a man in a balaclava smashing your neighbour’s car like a lunatic. More often than not, what you’re hearing is the work of one thing: the humble shock sensor.
How Do Shock Sensors Work?
Magnetic Shock Sensor
The most common type is the magnetic shock sensor. It’s about as simple as it sounds: a magnet suspended by an elastic band sits next to a coil. When the magnet vibrates, it induces a small electrical current in the coil, and that current tells your car alarm to start screaming.
Sensitivity Adjustment
Most shock sensors include a sensitivity screw so installers can dial them up or down. Some models even have dual zones:
Zone 1: Super-sensitive, usually makes the alarm chirp as a “warning” for light vibrations.
Zone 2: Less sensitive, but when triggered it sets off the full alarm.
Why Have a Shock Sensor?
On paper, they sound great. The idea is that they’ll protect your paintwork from scratches, dents, or vandalism.
In reality? Constant false alarms just annoy everyone around you, and might even tempt someone to actually key your car out of spite.
Even Mongoose admits in one of their installation manuals:
“Avoid over sensitivity as people nearby may not respond due to too many false alarms. (This type of sensor may not prevent wheel theft, we therefore advise the fitment of locking wheel nuts).”
Not exactly a glowing endorsement.
What Causes False Triggers?
Pretty much anything that makes your car vibrate:
Resonance in a multi-storey car park
Motorbike exhausts
Loud car stereos or exhausts
Even heavy trucks rumbling past
In short: the environment your car is parked in often matters more than the sensor itself.
Why Do So Many Alarms Come With Them?
Simple: they’re cheap to make, and easy for manufacturers to sell under the illusion of “extra protection.”
The truth is, there’s very little you can do to protect the outside of your car without triggering constant false alarms. If you’re worried about wheel theft, a tilt sensor is far more effective.
The “Intelligent” Shock Sensor Myth
Manufacturers love to talk about “Intelligent Shock Sensors.” Sounds fancy, right? But in practice, they all suffer the same flaws.
A thief isn’t going to bang on your windscreen to test it, but I do know of a case where an installer cracked a customer’s windscreen while testing one.
Intelligent, hey?
The Bottom Line
Shock sensors are cheap, noisy, and unreliable. They’re the number-one reason people ignore car alarms altogether.
If you actually want reliable security, look beyond shock sensors. Tilt Sensors, Glass-Break Detectors, and Ultrasonic Sensors all provide far better protection, without turning your car into the neighbourhood nuisance.
Check out the Alarm Sensor page for a breakdown of how different sensor work.
