this is a highly recommend car alarm essential and can be used with many other car alarms and car alarm accessories.Remote keyless systems operate by radio signal waves on a specific frequency. The range is either measured from the skin of the car or from a nominal central point.The system signals that it has either locked or unlocked the car usually through some fairly discreet combination of flashing vehicle lamps, a distinctive sound other than the horn, or some usage of the horn itself. The functions of a remote keyless entry system are contained on a key fob or built into the ignition key handle itself. Buttons are dedicated to locking or unlocking the doors and opening the trunk (or, on sport utility vehicles and station wagons, unlock/open the rear tailgate). Some cars will also close any open windows and roof when remotely locking the car. Some cars' engines with remote keyless ignition systems can be started by the push of a button on key fob. Some remote keyless fobs also feature a red panic button which activates the car alarm as a standard feature. For offices, or residences, the system can also be coupled with the security system, garage door opener or remotely activated lighting devices. (In point of fact it is a computer in the car which is programmed in the process, not the fob itself.) In general, the procedure is to put the car in 'programming mode'. Trunk release On cars where the trunk release is electronically operated, it can be triggered to open by a button on the remote. It is sometimes called hands-free. It is commonly found on European and Japanese luxury vehicles, such as Mercedes-Benz, Audi and Nissan. The vehicle can be unlocked and driven without the driver needing to physically push a button on the key fob to lock or unlock the vehicle and Conventionally, the trunk springs open with the help of hydraulic struts or torsion springs, and thereafter must be lowered manually. Modern systems implement encryption to prevent car thieves from intercepting and spoofing the signal. The range around the vehicle is not linear as corner pillars and small window apertures attenuate the signal, hence reduces its range. Programming Remote keyless entry fobs emit a radio frequency with a designated, distinct digital identity code. Inasmuch as "programming" fobs is a proprietary technical process, it is typically performed by the automobile dealership. Premium models (like SUVs with tailgates which are possibly out-of-reach for some) may have a motorized assist that can both open and close the tailgate for easy access and remote operation. This usually entails engaging the power in the car several times while holding a button or lever. It may also include opening doors, or removing fuses. The procedure varies amongst various makes, models, and years. Once in 'programming mode' one or more of the fob buttons is depressed to send the digital identity code to the car's onboard computer. Range testing The operating range of keyless remotes varies widely between manufacturers. E.g., Ford use 20m for Europe and North America and 5m for Japan and other markets where the transmitted power restrictions are much greater. The computer saves the code and the car is then taken out of 'programming mode'. As RKS fobs have become more prevalent in the automobile industry a secondary market of unprogrammed devices on sites like Keyless ride have sprung up. Some web sites sell steps to program fobs for individual models of cars as well as accessory kits to remotely activate other car devices. advanced Key Some cars have a proximity system that is triggered if a key like transducer (Advanced Key) is within a certain distance of the car.