Security system and method

A security system for a vehicle having a security mechanism, the system comprising:

• a transceiver coupled to the security mechanism, the transceiver having one transmission channel for transmitting a command signal in a first frequency band and a plurality of reception channels for receiving unlock signals in a second frequency band, said second frequency band being substantially higher in frequency than said first frequency;
• and,
• a remote radio-frequency transponder key having a plurality of transmission channels in said second frequency band and a reception channel in said first frequency band matched to the respective reception and transmission channels of the transceiver, the transponder key being arranged to transmit an unlock signal to the transceiver in response to valid reception of the command signal, the unlock signal being verified by the transceiver as valid before actuating the security mechanism,
• wherein the transceiver is arranged to select a channel within said second frequency band for reception of the unlock signal and to embed the identity of the selected channel in the command-signal, such that the transponder key transmits the unlock signal using the selected channel.