Idea:

1. Turn your iOS/Android device into a measuring tape that's not a pain the ass to use.

How:

2. Build a package of three battery powered devices that come packaged together and pair with a custom app on the iOS/Android device. Devices pair with the phone via BlueTooth, and emit noise outside the range of human hearing, one freq for each device. Devices come with instruction to place them at known (user adjustable) distances from each other in an equilateral triangle. (Use 4 devices and form a tetrahedron?) iOS/Android device listens to emitted noise to calculate its position relative to the devices. The App calculates and remembers the positions of the phone, so you can ask it to give you x,y,z and hypotenuse distance between whatever points you ask of it.

Result:

3. PROFIT