Everybody knows about using a cell phone for GPS, speedo, streaming music, or even to make a phone call but I recently came up with some others. I was at a friend's house who had an bore scope and I thought that was pretty interesting so I bought a USB endoscope for my cell phone. The only difficulty was finding the app that produced the best resolution but I found a good free app and now I have a bore scope/endoscope that cost me about $20! Literarymadness came up with another use for the endoscope and that was to be able to read the numbers stamped on my flywheel. They are small and my eyes have a hard time reading them from even as close as I can get to it. Another use would be to inspect the inside of a frame.
I was watching some videos on using a leakdown tester on youtube and some of people used a microphone to amplify the sound of air leaking so I thought a microphone would be another good addition to my cell phone. I got the mic from Amazon for about $6 and found a free app that routes the sound to the cell speakers, provides graphical sound wave, and supposedly will record the sound (I haven't tried that yet). It is very sensitive such that I have to worry about reverb as well as how noisy it is in the garage (eg. the compressor must not be running!).
Can anybody come up with new uses for those tools or other tools you can use with a cell phone?