I read a review for an app called Power Nap HQ, and it seemed interesting: it took nap data, based on your movements. You entered how much time you wanted to sleep, set a backup alarm, chose a sequence of sounds, and laid it next to you. It would report back on your movements, indicating the depth of the nap, and it would also record any abrupt sounds you made. Nicely designed, too. A buck. Bought it.
Read the whole thing. You can never go wrong reading Lileks.