An astonishing microwave radar sensor with send and receive antennae printed on each side of the board. You can use this without a micro-controller, powering it directly with anything from 4V to 28V. Hook it up to a power source and the output pin will go logic-high for 2 seconds when the antennae detect a radar "ping". On the rear of the board you have 3 additional configuration options:
C-TM: Adjust repeat trigger time (default 2 s). Adding a capacitor will give a longer repeat trigger time.
R-GN: Detection distance adjustment (default 7 m). Adding a resistor the detection distance will become shorter. If connected with a 1-MΩ resistor, detection range is about 5 m.
R-CDS: By adding a resistor (in parallel with the internal 1-MΩ resistor), you can change the light detection threshold. Applicable only when a light sensor is soldered in its pads (CDS) on the front of the circuit board (See below).
Hook it up to a micro-controller and the scope is endless. A diy datasheet here : https://img.filipeflop.com/files/download/Datasheet_rcwl-0516.pdfAnother Arduino example. http://www.handsontec.com/dataspecs/sensor/radar-sensor.pdf I use 4 to control different zones for garden lighting. I have a 12V supply to these sensors and they have an built-in on-board 3.3V buck converter to power my micro-controllers. It even has a spot on the board to solder a Light-dependent-resistor so that it only triggers the output pin during darkness. Really, it really couldn't get any more useful unless it fetched your beer. Great video below showing just how simple it is to use. Just copy and paste link below onto a new browser.
https://www.youtube.com/watch?v=IJoPkKlxFXA