Shock Sensors and False Alarms

Watch out for the Fat Man in a Balaclava!

Shock Sensors are beyond doubt the main culprit when it comes to false alarms.

How many times have you got annoyed at a car alarm going off for no obvious reason?

More to the point, have you ever gone out to check and see if your neighbour’s car is actually getting broken into? Let alone catching a man in a balaclava hitting your car like an imbecile?

Don’t cry wolf!

If you think that getting an alarm with a shock sensor is a good idea then watch this video:

How do Shock Sensors Work?

Magnetic Shock Sensor

The most common impact sensor is the magnetic shock sensor. It is simply a magnet held by an elastic band which is suspended next to a coil. When the Magnet vibrates it induces electricity in the coil. This, in turn, triggers your car alarm to go off.

Sensitivity Adjustment

These sensors have a sensitivity screw which can be dialled up and down. This is used to adjust how much vibration is required before your alarm sounds. Some have a dual zone setting.  The 1st zone being more sensitive will tell the alarm to chirp a couple of times as a warning should a small vibration be detected. The 2nd less sensitive zone will trigger a full alarm.

Other types of impact sensors

There are other other types of shock sensors out there which I’m not going to explain here (piezo sensors for example). These sensors need more understanding of electronics so are not going to make sense unless you are into it. You can do your own homework if you really are interested!

What you should know is that all shock sensors deliver similar results. They pick up vibrations to set your alarm off.

Why have a Shock Sensor?

The reason many people think they are a good idea is that they don’t want their car’s bodywork to get scratched or dented. The reality is that constant false alarms piss everyone off will probably be the motivation to actually take a key to your paintwork!

The irony is that the act of keying a cars paintwork is unlikely to be picked up by the shock sensor!

It’s also unlikely that the use of a screwdriver to remove your number plates or exterior accessories will be detected by the shock sensor.

Here is a quote from the Mongoose installation manual:

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)

So what will cause a shock sensor to trigger?

There are many things that can cause the sensor to vibrate. The environment the car is located is often a big factor. For example, a car parked in a multi-storey car park is very susceptible to the resonating frequency of motorcycle exhausts, or even loud car exhausts for that matter.

Cars parked on the roadside can pick up vibrations from trucks and buses passing. In Windy Wellington, the wind can also play havoc with them.

The location of the shock sensor in a vehicle is also a major factor. In theory, the best location for one is the centre of the vehicle so it is not biased to one side. Yet most of the ones I have removed are tied to the steering column!

So why do so many alarms come with Shock Sensors?

First off is that they are cheap to manufacture. Secondly is a false notion that they will protect your car from getting damaged. The reality is there is not much that can be done to protect the outside of your vehicle without false alarms. If you want to protect your wheels then a tilt sensor will be far more effective.

What about Intelligent Shock Sensors?

I have read all sorts of marketing bullshit about “Intelligent” shock sensors. Some alarms have them built into the brain which makes the ideal centre of the vehicle location impossible in most cases!

The reality is that a car thief is not going to bang on your windscreen to set it off. But I do know if a case where an installer has cracked a windscreen doing this test!

Intelligent hey!

About Julian

Owner and Installer at Obsessive Vehicle Security Limited. More details here... Please keep Comments relevant to the post and use the Contact form for enquiry's
This entry was posted in Alarm Accessories, Car Security, Sensors, Trouble Shooting! and tagged , . Bookmark the permalink.

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