A detection system adapted and configured to detect an illegal use of a personal wireless communication device , comprising: - a plurality of peripheral control units , each installed, or intended to be installed, in a respective indoor space (c1, c2, ..., cN) to be monitored; - a central control unit operatively connected to the plurality of peripheral control units , preferably by means of Modbus TCP protocol; wherein each peripheral control unit comprises: - a radiofrequency signal detector adapted and configured to pick up electromagnetic radiations transmitted and/or received by the personal wireless communication device in an operative frequency spectrum and to generate a detected electrical signal related to such electromagnetic radiations; - a processing unit operatively connected to the radiofrequency signal detector for receiving the detected electrical signal, wherein the processing unit is adapted and configured to analyze the detected electrical signal and to generate at least one alarm message if it determines that the detected electrical signal meets at least one alarm condition; - a communication interface adapted to operatively connect the peripheral control unit to the central control unit to allow the alarm message to be sent to the central control unit ; wherein the processing unit is adapted and configured to: - analyze a plurality of separate portions (S1-S5) of frequency spectrum (FS) of the detected electrical signal; - determine that said alarm condition occurred if it detects that a difference in a measurement of power and/or amplitude of the electrical signal exceeds a first threshold value in at least two consecutive time analysis periods of a same portion (S1-S5) of frequency spectrum (FS) . - a plurality of peripheral control units , each installed, or intended to be installed, in a respective indoor space (c1, c2, ..., cN) to be monitored; - a central control unit operatively connected to the plurality of peripheral control units , preferably by means of Modbus TCP protocol; - a radiofrequency signal detector adapted and configured to pick up electromagnetic radiations transmitted and/or received by the personal wireless communication device in an operative frequency spectrum and to generate a detected electrical signal related to such electromagnetic radiations; - a processing unit operatively connected to the radiofrequency signal detector for receiving the detected electrical signal, wherein the processing unit is adapted and configured to analyze the detected electrical signal and to generate at least one alarm message if it determines that the detected electrical signal meets at least one alarm condition; - a communication interface adapted to operatively connect the peripheral control unit to the central control unit to allow the alarm message to be sent to the central control unit ; wherein the processing unit is adapted and configured to: - analyze a plurality of separate portions (S1-S5) of frequency spectrum (FS) of the detected electrical signal; - analyze a plurality of separate portions (S1-S5) of frequency spectrum (FS) of the detected electrical signal; - determine that said alarm condition occurred if it detects that a difference in a measurement of power and/or amplitude of the electrical signal exceeds a first threshold value in at least two consecutive time analysis periods of a same portion (S1-S5) of frequency spectrum (FS) . <EOS>