Based on a request, I have put this together as a complete How-To on the ArduinoInfo.Info WIKI HERE: It looks like this:
This is simple: An Arduino/YourDuino, an UltraSonic Sensor and a beeper. Example code is provided.
It senses the distance to objects up to 2 M (6 feet) in front of the sensor and produces audio beeps that denote the distance. There are 3 zones with beeps getting faster in each zone and then switching to a high tone in the next zone. The last 25 cm can sense small differences down to about 2 cm.
The usual problem is taking something that works, like this: and packaging it so it is portable and will stand up.
I am always lurking through Walmart and Home Depot etc. looking for Stuff That Could Become Arduino Parts.
At Walmart I found the $3.77 waterproof lantern used in this project. It could be used for lots of other Arduino-based projects that need an outdoor case, batteries and maybe an on-off switch. Like remote temperature / humidity / Other sensing with an nRF24L01 radio, Wildlike sensor / Camera control. Etc. Etc. If anyone makes a project based on that case, please let me know and I'll add it to the ArduinoInfo.Info WIKI:
Also, this project is now linked to a section called Understanding the Science Behind the Ultrasonic Distance Sensor (click): That in turn links to Educational Lesson Plans and a SlideShow that can be used in the classroom (My wife is still updating that). If anyone uses this in a class or helps a teacher do this please let me know. I may make a low-cost parts kit available.
Any feedback or suggestions appreciated!