What is a passive alarm system?

A passive alarm system is a system, primarily found in cars, that activates automatically when the key is removed from the ignition. Alarm features may include sounds, flashing lights, ignition cutoff, proximity sensors and more and are enabled without the active participation of the driver.

While passive alarm systems offer more protection, as they don't rely on the memory of the driver to activate them, they can also prove to be an annoyance, as drivers are more likely to set them off accidentally. Insurance companies frequently offer discounts for drivers who have cars with alarm systems, and a passive alarm system is often a requirement for this discount as the car is always protected by the alarm.