A radio frequency motion sensor comprising: a radio frequency transmitter, the transmitter configured to emit radio frequency pulses; and a switched receiver configured to receive reflected ones of the emitted radio frequency pulses, the radio frequency transmitter comprising: a pulse generator (408, 508) configured to generate signal pulses; a dielectric resonator oscillator (406, 506) configured to generate a stable radio frequency oscillating signal; a switched circuit coupled to the pulse generator and the dielectric resonator oscillator, the switched circuit configured to generate a pulsed radio frequency oscillating signal that is modulated by the signal pulses of the pulse generator and whose dominant frequency is derived from the dielectric resonator oscillator, characterized in that the switched receiver comprises a homodyning magnitude detector receiver that is switched in accordance with a timing signal from the pulse generator, wherein said homodyning magnitude detector receiver is switched on for a duration of time T at a first offset time from a nominal start time of a signal pulse, resulting in a first receive level (t0 Receive Level), and is switched on for a duration of time T at a second offset time from the nominal start time of the signal pulse, resulting in a second receive level (t1 Receive Level), an intermediate frequency amplifier configured to amplify the output of the homodyning magnitude detector receiver, a synchronous demodulator configured to receive the output of the intermediate frequency amplifier and to detect the difference between the first receive level and the second receive level, a baseband circuit configured to amplify and subsequently filter the output of the synchronous demodulator to provide a measure of movement of the human body. a radio frequency transmitter, the transmitter configured to emit radio frequency pulses; and a switched receiver configured to receive reflected ones of the emitted radio frequency pulses, the radio frequency transmitter comprising: a pulse generator (408, 508) configured to generate signal pulses; a dielectric resonator oscillator (406, 506) configured to generate a stable radio frequency oscillating signal; a switched circuit coupled to the pulse generator and the dielectric resonator oscillator, the switched circuit configured to generate a pulsed radio frequency oscillating signal that is modulated by the signal pulses of the pulse generator and whose dominant frequency is derived from the dielectric resonator oscillator, a pulse generator (408, 508) configured to generate signal pulses; a dielectric resonator oscillator (406, 506) configured to generate a stable radio frequency oscillating signal; a switched circuit coupled to the pulse generator and the dielectric resonator oscillator, the switched circuit configured to generate a pulsed radio frequency oscillating signal that is modulated by the signal pulses of the pulse generator and whose dominant frequency is derived from the dielectric resonator oscillator, characterized in that the switched receiver comprises a homodyning magnitude detector receiver that is switched in accordance with a timing signal from the pulse generator, wherein said homodyning magnitude detector receiver is switched on for a duration of time T at a first offset time from a nominal start time of a signal pulse, resulting in a first receive level (t0 Receive Level), and is switched on for a duration of time T at a second offset time from the nominal start time of the signal pulse, resulting in a second receive level (t1 Receive Level), an intermediate frequency amplifier configured to amplify the output of the homodyning magnitude detector receiver, a synchronous demodulator configured to receive the output of the intermediate frequency amplifier and to detect the difference between the first receive level and the second receive level, a baseband circuit configured to amplify and subsequently filter the output of the synchronous demodulator to provide a measure of movement of the human body.