* The given range concerns opened area i.e. perfect conditions without obstacles. If between the transmitter and the receiver obstacles are found, range decrease can be expected depending on the following: wood and plaster from 5 to 20%, brick from 20 to 0%, rmed concrete from 40 up to 80%. As for metallic obstacles the application of radio system is not recommended due to an enormous operation range decrease. Also overhead and underground power lines have a negative influence on the operation range as well as transmitters of the GSM network placed in a short distance of devices.