They could probably do even better by getting the phone to emit a loud clapping sound, approximating a dirac delta so they could measure the impulse response of the room. The fourier transform of that should have some nice distinctive shapes. On the other hand, that wouldn't be nearly as unobtrusive, and most smart phones have crappy speakers, so you wouldn't get much response.

I used CLEPs for 30 credits of a double B.S. including almost all of my general education requirements. The key with getting most universities to accept CLEPs -- which are mostly targeted at people coming out of highschool with some college level experience -- is to make sure that you haven't taken an official college level course in the department that you plan to CLEP in. I CLEP'd out of literature, american history, sociology, american government, composition, economics ... Basically everything I could. Take AP exams for everything you can as well. I still wound up having to take a couple of classes outside of math and computer science in order to fulfill art and cross-cultural coursework requirements -- the one that stuck out most was african american theatre -- but overall I can't say I'm any worse off for having given the other departments their pound of flesh.

I did have to study for the CLEPs I took to ensure I passed them all, but I was much happier studying sociology for a weekend than for a semester.

The last time after I found myself seriously entangled with a girl, she couldn't stand to be in the same state with me.

*ducks*