> The hands-free card also called “badge”, is able to replace both the traditional remote control locking command and the ignition key. When the driver is carrying the card, you only needs to place your hand on the door handle to unlock the car. you don't even need to take the card out of his pocket or bag.
The card is equipped with a memory for vehicle and user data
For each driver, the position of the seats is memorised, as are
other comfort elements such as air conditioning or car radio
As well as a transponder, the hands-free card contains electronic features for low-frequency communication.
To ensurethis radio link, the car contains several aerials dissimulated in
the external door handles or in the roof trim. When the
infrared sensor on a door handle is solicited, the computer
emits a series of very short encoded bursts. When the card
detects this emission, it sends back a code to signal its presence.
An encrypted dialogue is then set up between the computer and the card.
These two elements identify themselves
to each other through a complex exchange of digital messages.
Both the computer and card contain encryption algorithms based on mathematical operations.
To check that the card is indeed the one attributed to the car,
the computer sends a number to the card. At the same time,
it calculates the reply to be sent using its own algorithm and encryption key.
On receiving the number, the card calculates a result in turn
and transmits it to the computer. As the card and the computer have the same algorithm and the same key,
the two results must be identical. If they are, the computer is certain that
it has identified the card. This dialogue only takes 80 milliseconds.
Door unlocking and engine starting are then authorised. In order to prevent accidental unlocking if the user
remains near the car, this operation is only effective if the user takes hold of one of the door handles.
The system detects this gesture using infrared sensors located in the handles and authorises unlocking.
The command to lock the
doors is given either when the user orders it by means of the remote control,
or on some vehicles when the distance separating the card from the vehicle is too great for the radio link
to operate. In this case, the computer detects an “absence of response from the card”.
To start the engine, the computer dialogues again with the card to confirm its presence in the passenger compartment. If
such is the case, the engine is started by pressing the “start” button.