The block for the microwave gate working on 24GHz was developed together with Radan s.r.o. company. The signal received from the doppler sensor with Gunn’s diode is amplified, filtered and digitalized by the AD converter and processed by computing means of CPU ATMega128. The amplitude of the TX signal is modulated by 1kHz frequency. The RX block together with FFT algorithm evaluates the spectrum and compares it with the threshold. The alarm is set up if the spectrum is modified by the intruder.