A motion/vibration sensor includes a transmit/receive antenna unit, an oscillation unit and a frequency-mixing unit. The transmit/receive antenna unit receives an output signal from the oscillation unit and transmits a detection signal toward at least one object. The detection signal is reflected by the object as a reflected detection signal and received by the transmit/receive antenna unit. The oscillation unit receives the reflected detection signal from the transmit/receive antenna unit for self-injection locking and the frequency-mixing unit receives the reflected detection signal from the transmit/receive antenna unit for frequency demodulation. The frequency-mixing unit mixes and demodulates the reflected detection signal from the transmit/receive antenna unit with the output signal from the oscillation unit into a baseband output signal which represents a motion/vibration information.
