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The presented paper focuses on the possibilities of technical methods designed to detect a trespasser under the ground,
and in general on the possibilities of detection a trespasser behind an obstruction. The paper analyses method of
detection of a trespasser that were practically verified by the author of the paper. The first part of the paper discusses the
characteristics and use of piezoelectric films that could be used as a replacement for the traditional geophone for
detection of underground mining operation. It also provides a block connection diagram of the measuring chain and
photos of the practical implementation of the sensor. The consequent part of the paper then discusses the possibilities of
detecting a trespasser based on electromagnetic waves emission by humans in the ELF - Extremely Low Frequency
band. The paper is supplemented with illustrative photos and results of numeric processing of signals in the form of
graphs and courses.
The history of excavating and using tunnels spans long into the past. Tunnels were used not only as storage for food and
war material but mainly as effective means of protection against attackers. A significant motivating factor for
constructing tunnels lies in the hidden possibility of movement of people and transfer of material under the ground of a
protected perimeter. At present some tunnels are used as roads for smuggling drugs, weapons, ammunition or illegal
passages of people. There are even cases, not exceptional, when tunnels were excavated with the aim to rob a bank safe
etc. The fact that construction of tunnels, often quite primitive ones, is not sporadic, can be continually documented not
only by historical sources but often also by the daily news summary. The concurrent lack of proper technological means
results in the renaissance of using tunnels for illegal purposes even at present. The presented paper focuses on the above
mentioned area and points to little used physical principles of detection underground activities of trespassers.
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