  The ultrasonic motion detector devices emit ultrasonic sound energy into an
area of interest (monitored area), and this further reacts to a change in the
reflected energy pattern. The system uses a technique that is based on a
frequency shift in reflected energy to detect a movement or change in position
(motion). In this system, ultrasonic sound is transmitted from the transmitting
device which is normally in the form of energy. The transmitted sound utilizes
air as its medium and this travel in a wave type motion. The wave is reflected
back from the surroundings in the room/hallway and the device hears a pitch
characteristic of the protected environment. In this system, the wave pattern
is disturbed and reflected back more quickly, thus increasing the pitch and
signaling an alarm whenever motion is detected. The main contribution of this
work is the design of a circuit that can sense motion through movement of
anything, a low cost and portable motion detector, and the design of a circuit
that can be used to trigger another circuit whether to ON or OFF depending on
the circuit attached to it. Generally, the design is made to detect movement or
moving object in a an enclosed area. In this work, a transmitter transducer
generates a signal at a frequency of 40khz, and when the signal is blocked by
any moving object, and this in turn, triggers a buzzer via a timing circuit.
This system works on the principle of the signal interference by a moving body,
and the system is dependent on the presence of an intruder or moving object
within a monitored area. The system after design and construction was tested
and found to work in accordance with specifications.
