Bergerab made this Instructables detailing the build of his DIY pocket-sized ultrasonic ruler:
Today everything is digitalized. Most of us don’t bother to waste our time using maps, going to the record store, or even going to the DVD store anymore. So… why are so many people using tape-measures and rulers? Yes, they are reliable, but they are certainly not convenient. With innovations, such as ultrasonic range sensors, we have entered a time where you don’t have to bother getting out your old tape-measurer. Using this pocket-sized ultrasonic ruler, you can simply point at any object, click a button, and the distance will be displayed on the 8 LED display. And you don’t have to pay hundreds of dollars, like most commercially available ultrasonic measurers. This ruler is the smallest (5cm by 7cm) and cheapest (about 5 USD) ultrasonic measuring device available today.