The ESP8266 microprocessor from Espressif Systems is an incredible little device. It is a WiFi system on a chip that integrates all of the radio circuitry including filters, low noise receiver amplifier, antenna, and RF balun all in a neat tiny package. It's real easy to program and powerful enough for complex projects.
Dan Wilcher has developed a super simple tutorial on using the ESP8266 and MicroPython to build a WiFi Network Scanner.
This tutorial is great for beginners and those who are looking to dip their feet into the world of micro-controllers. Using only three components: an ESP8266, an LED and a analog meter, you can build a WiFi scanner than can be used to trouble shoot or hunt out WiFI access points.
Best of all, the entire code base for the project is 11 lines long.
You can find all you need to build your own ESP8266 WiFi Scanner here.