Reported Problem: Aftermarket Car Alarm Keeps Going Off!
Probably thee #1 reported problem in the history of car alarms is the complaint of the car alarm going off at all hours of the day and night. This would clearly be the most annoying problem you could have with a car alarm and for your neighbours!
Technically, the problem can be from a small list of causes, but fortunately most of the time, it's only due to a sensor being set to sensitive during installation or it just needs a slight adjustment after being in the vehicle after several years. And commonly the #1 culprit is known as a "shock-sensor" or "impact-sensor". These types of sensors as you can guess, detect specific levels of vibrations caused through the vehicle.
When these sensors are set to sensitive (like when an alarm installer tries to use a shock sensor as a glass break detector, which it's not meant to be used for, there are specific sensors for that) the alarm can false trigger with just the wind blowing against the vehicle, when a loud vehicle or motorcycle drives by it or even if a cat walks across the hood!
Shock/impact sensors are only meant to detect larger vibrations or impacts made to the vehicle. Examples would be vibrations caused by another vehicle backing into the vehicle, jacking-up or towing, or if someone literally took a baseball bat or a brick against the glass. Detection for any lighter vibrations made to the vehicle would require a different type of sensor.
The fix: A system's shock sensor is commonly found mounted under the driver's dash area (a.k.a. foot-well area). Usually they are mounted snugly against some factory wiring using a nylon zip-tie. The sensors can range in size from a 2" by 2" small plastic box to almost the size of a pack of cigarettes. They will also have a small 3 or 4 wire plug plugged into it. And, most of these sensors have color LED's built into them that will light up when you tap your finger on them.
When you think you found the sensor, look on the sides of the sensor and you will find either a small adjustment screw in a small hole or on some older systems a protruding adjustment knob sticking out the side of it (a.k.a. thumb pot adjuster that you can turn just using your fingers. The type found through a hole in the sensor is a small eye-glass phillips screw). No matter which type of adjustment you have they all adjust exactly like a volume knob. Turning it clockwise makes the sensor more sensitive (volume up) and counter-clockwise makes it less sensitive (volumn down).
The best way to begin the adjustment of a shock sensor is to turn the sensor all the way down (counter-clockwise) and then slightly turn it up 1/4 of the way. Now, to test the sensor's sensitivity; roll the driver's side window down, close all the doors and arm the system. Wait a minute, then reach in through the open window and bounce the side of your fist off the steering wheel (not excessively hard). Some sensors that are known as a "2-stage" sensor will just pulse the vehicle's horn or the system's siren. This is known as the "warn-away" response. If the sensor either sounds the warn-away signal or does not sound at all (sensors with single-stage sensing) this will probably be a good setting to leave it at and no further adjustment will be neccassary. Now if the system still false triggers, you'll want to try a lower setting or isolate the sensor from the system completely which is done simply by unplugging the plug from the sensor.
If the system still triggers after you unplug the sensor you know its not the shock sensor causing the false triggering. But if it only falses with the sensor plugged in and after several attempts of making adjustments, you have a bad sensor that needs replacing.
