The present invention provides a portable device, comprising first
identification means for wireless transmission and/or reception of
electromagnetic radiation for the purpose of identification thereof, in
addition to a system, comprising: a transmitter for wireless transmission
of electromagnetic radiation with at least a first frequency, a portable
device and a receiving circuit for wireless reception of electromagnetic
radiation, wherein a change occurs in the electromagnetic radiation
received by the receiving circuit when the device is located in the
vicinity of the receiving device.