Abstract: The apparatus of the invention includes a collapsible antenna for detecting the electric field associated with the individual. A current-to-voltage operational amplifier is coupled to the antenna. The amplifier includes an inverting input, a non-inverting input, and an output. A magnetic feedback path is provided for the amplifier. A magnetic filter is positioned between the amplifier output and the inverting input of the amplifier. An optical coupler is connected to the output of the amplifier. An intruder indicator, such as a signal display apparatus, a signal processor, or an audio indicator is connected to the optical coupler. The intruder indicator may simply provide a signal that an intruder is present or it may provide additional data defining the nature of the intruder.