In this paper, an innovative and highly optimal triple layer Wireless Sensor Network (WSN) system is analyzed and illustrated, which monitors M-ary events like temperature, pressure, humidity, etc. with the help of geographically distributed local sensors. These local sensors are made to convey signals to the fusion centre using M-ary Frequency Shift Keying (MFSK) modulation scheme over Rayleigh fading channels. At the fusion centre, coherent detection aided by Maximal Ratio Combining (MRC) takes place. With the help of various simulations, the performance and efficacy of the system has been analyzed by varying modulation levels, number of local sensors and probability of correct detection by the local sensors. Our study endeavours to prove that MFSK WSN is a highly reliable system, which is capable of correct detection of M-ary events even if the channels are highly dynamic and the sensors are faulty.