Relays can be used in many different ways but are most commonly used for high amp applications, such as Car Alarms, Remote Starts, HID Headlights, Strobe lights, Fog Lights, Stereos, Air Ride Suspensions, Fans, Air Horns, and so much more. A trigger can be anything from the accessory or ignition circuit to a switch which provides a positive or negative trigger. Here are some of the things you can do with a car alarm: Turn on your radio, lights, the lighting under your car, remote start, trunk pop, reverse polarity, door locks, doors pop, dome light, horn honking, and much more. Some functions will require additional parts to work. These are just a couple of examples on what installers will use relays for. They can even be used with your aux output from your car alarm!
We recommend getting at least 4 relays for your car alarm installation. It is better you get them here for a lot less than get charged an arm and a leg at a shop.