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How do Keyless Remotes Work?

How Do Keyless Remotes Work?

 

Keyless remotes contain a short-range radio transmitter, and must be within a certain range, usually 5–20 meters (15–60 ft), of the car to work. When a button is pushed, it sends a coded signal by radio waves to a receiver unit in the car, which locks or unlocks the door. Most RKEs operate at a frequency of 315 MHz for North America-made cars and at 433.92 MHz for European, Japanese and Asian cars. Modern systems implement encryption to prevent car thieves from intercepting and spoofing the signal. Earlier systems used infrared instead of radio signals to unlock the vehicle, such as systems found on Mercedes-Benz, BMW and other manufacturers.

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. A typical setup on cars is to have the horn or other sound chirp twice to signify that the car has been unlocked, and chirp once to indicate the car has been locked. For example, Toyota, Scion, and Lexus use a chirp system to signify the car being locked/unlocked. While two beeps means that driver's door is unlocked, four beeps means all doors are unlocked. One long beep is for the trunk or power tailgate. One short beep signifies that the car is locked and alarm is set.

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 tailgate. On some minivans, the power sliding doors can be opened/closed remotely. Some cars will also close any open windows and roof when remotely locking the car. Some remote keyless fobs also feature a red panic button which activates the car alarm as a standard feature.

Some cars' engines with remote keyless ignition systems can be started by the push of a button on the key fob.

On cars where the trunk release is electronically operated, it can be triggered to open by a button on the remote. Conventionally, the trunk springs open with the help of hydraulic struts or torsion springs, and thereafter must be lowered manually. Premium models, such as SUVs and estates with tailgates, may have a motorized assist that can both open and close the tailgate for easy access and remote operation.

For offices, or residences, the system can also be coupled with the security system, garage door opener or remotely activated lighting devices.

 

Range

The operating range of keyless remotes varies widely between manufacturers. E.g., Ford uses 20 m for Europe and North America and 5m for Japan and other markets where the transmitted power restrictions are much greater. The range is either measured from the skin of the car or from a nominal central point.The range around the vehicle is not linear as corner pillars and small window apertures attenuate the signal, hence reducing its range.

range-plot.jpg

 

Source - Wikipedia