Patent ID: 7088236

Claim:
A surveillance system comprising at least one transmitter, each being adapted to transmit an electromagnetic signal, and at least one receiver, each being adapted to receive a signal, said system being further adapted to: transmit a first electromagnetic signal by use of one of the at least one transmitters, transmit a second electromagnetic signal, succeeding the first signal, by use of one of the at least one transmitters, receive said first signal by use of one of the at least one receivers, receive said second signal by use of one of the at least one receivers, the system further comprising a comparing device that compares the received first signal and the received second signal in order to detect a difference, if present, in said two signals, said difference being caused by a physical change present in the signal path between at least one of the transmitting transmitters and at least one of the receiving receivers, said change occurring between initiation of transmittal of the first signal and termination of the receipt of the second signal, wherein the transmitter(s) and the receiver(s) are components of a wireless network used for data transmission.