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      05-08-2013, 08:41 PM   #7
BMWrules7
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Quote:
Originally Posted by dbs600
Quote:
Originally Posted by The X Men View Post
You could have use your mechanical key to open the door as well.
OMG, you're absolutely right; how stupid of me!

Otherwise, thanks for your replies, gentlemen. I'm just wondering what's occurring when the remote doesn’t work, but placing next to the steering wheel brings it back to life; maybe these charge up as well - but only for a short amount of use thereafter?




No. As the previous poster said, there key fob contains a passive RFID chip.

Normally, the key fob transmits the secret information by way of a small, low power, RF transmission.

This way, you can keep the key fob in your pants pocket. The key fob silently listens for a request from your car after you pull the door handle, for example.

Once the key fob receives a request (listening takes far less battery power than transmitting), the key fob returns, among other things, the encrypted value if your key's ID. Then, in near real time, your vehicle evaluates the response from the key fob and ensures the decrypted value matches the expected value in the car's key database. Every key has their own ID. The key fob has the capability to handle non-key related functions, such as the number of miles on your vehicle.

So long as your key fob has battery power, your key fob can convey its secret value in response to an active request from your car.

When the battery gets too low, the key fob conveys this condition to your car. In turn, a warning is displayed on your dash.

Now, at some point there may not be enough energy in the battery to power the transceiver. That's ok! A battery is not necessary! Since the RFID can be determined passively, you do not need power. All you have to do is place the key fob in close proximity to the car's reader. There RFID reader's location is marked on the steering wheel for your convenience. Just hold the key fob next to the reader and depress the start button. The RFID value is read and compared in a similar manner as an actual transmission. However, it may lack some level of full encryption used in a transmitting environment.

This does not mean there is no encryption. It just may be less than that used by the transmitter.
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