Abstract: A homodyne type radar for detecting intrusions into its field of radiation using the Doppler effect, working by pulses connected to an alarm device triggered in case of an intrusion. The output circuit of the pulse generator of the radar apparatus comprises a capacitor connected at the pulse frequency to a pulse generating and receiving circuit, the load variation of this capacitor controlling the alarm.The resistor is series connected to the emitter-collector circuit of a hyperfrequency transistor which is common to the pulse generating and receiving circuit.The cicuit connecting the capacitor to the alarm device comprises a low-pass filter and a step-apparatus.An oscillator controlling the pulse generating apparatus is also used to control a direct voltage to direct voltage converter when the power is supplied by a battery.