Not sure, but I wouldn't mind playing with one myself. I've always thought it would be amusing to hear what happens when you're asleep, be it from you or from anything in your environment. I had found one on my iPhone a while back, but it didn't work because my iPhone was old and had some issues (namely, in this case, the microphone didn't work from apps for some reason).
A very quick search brought me to this: http://www.androidzo...p time recorder
Some are completely different apps, but there were a couple that might do what you want. The first I saw was Spy Recorder that's $0.99.