Modular kit of a device contains the first and the second directional couplers (10, 11), which serve for extraction of two signals traveling in the opposite directions of the optical fiber and are interconnected via the optical coupling element (9) and the first optical filter (5) with the first photodetector (7), which is interconnected with the control unit (1) equipped with the wired communication interface (2) and/or the wireless communication interface (3), and powered by the power supply module (4). The output of the first optical filter (5) is connected to the input of the first photodetector (7) via the second optical filter (6), while the second output of the second optical filter (6) is connected to the input of the second photodetector (8). The output of the second photodetector (8) is interconnected with the control unit (1). Between the output of the first directional coupler (10) and the first input of the coupling element (9) is connected the third directional coupler (12) oriented identically as the first directional coupler (10), while its split branch is interconnected with the input of the third photodetector (14), the output of which is connected to the control unit (1). Between the output of the second directional coupler (11) and the second input of the coupling element (9) is connected the fourth directional coupler (13) oriented identically as the second directional coupler (11), while its split branch is interconnected with the input of the fourth photodetector (15), the output of which is connected to the control unit (1). The first optical filter (5) is a band-pass filter with wide bandwidth and its characteristics are such that the monitored signals are spectrally located at its leading or falling edge. The second optical filter (6) is a three-gate-type filter, where its one output corresponds to the band-pass function with the central wavelength corresponding to the wavelength of the first monitored signal, and its second output corresponds to the band-stop function and therefore the remaining optical spectrum is directed to it.