What Sets Off Car Alarms?

by Andy WaryckaUpdated August 16, 2023
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No one likes to be woken up by a car alarm in the middle of the night. Alarms can be triggered by everything from loud noises to tilt sensors to forgetting to disarm it before you open the car door. Here are some answers to FAQs about modern car alarm sensors to restore a little domestic tranquility to your block.

How Car Alarms Work

In its simplest form, a car alarm is nothing more than a simple computer, a sensor, a siren and a remote control unit on the key fob for arming and disarming the security system (https://itstillruns.com/deactivate-factory-car-alarm-7596833.html). When the sensor detects an intrusion or other input above a given tolerance, the alarm computer sets off the siren, which makes loud noises to deter the car thieves or vandals from continuing their work. More new cars have other features to prevent car theft, like immobilizers that prevent the car from starting, paging systems to alert the vehicle owner the alarm has been activated, and even the ability to arm and disarm the alarm over the internet.

It’s worth noting that car alarms can malfunction if the vehicle has low battery. If you find that your car alarm keeps sounding, take the vehicle to a mechanic. A dead battery will be an obvious reason for the alarm sounding, but it could be something like a faulty alternator or a connection issue.

Voltage Sensors

There are many different types of sensors for every type of alarm. Most basic alarms found in older cars use a single voltage sensor to determine when a theft or break-in attempt is being made. This sensor monitors the static voltage of the car's electrical system and triggers the alarm when it senses a drop in voltage, such as when a door or trunk is opened, which triggers the interior lights to go on. Attempting to start the car or cut the power will also trip the voltage sensor.

Shock Sensors

The most common form of sensor found in car alarm systems are motion sensors that detect when someone or something is attempting to move or gain access to the vehicle. Shock sensors come in single- and dual-stage form. Single-stage sensors only detect the heavy impact of a door being forced or glass breaking, but a dual-stage will chirp the siren as a warning at a light impact before setting the alarm off in full at a heavier impact.

These sensors are often subject to false alarms from animals jumping on the vehicle, the vibration of a heavy truck passing by, or loud noises such as stereos or loud exhaust. As a result, these sensors can typically be adjusted for sensitivity to reduce false alarms.

Hood Latch Sensors and Door Sensors

Simple switches can be placed on hoods, doors and trunks to activate the alarm when any of these are opened while the alarm is armed. When the door is opened, the switch closes and the alarm triggers the siren.

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