Ideally, I'd be able to make a mental note, just say "I feel about 70% energetic now", whenever I think of it, or at fixed intervals, and then call up all the data later and do some statistics on it. ("experience sampling", they call it.) But we can't do that mentally because we forget things; the best we can do (that I know of; do any of you readers know anything better?) is cell phone apps. And that takes about 10-15 seconds of overhead, it's kind of annoying, and I can't always do it easily (say, if I'm in a meeting). Pencil and paper is even worse.
The best feasible thing I can think of is a watch. We're used to watches, they're pretty unobtrusive, and if it has 5 buttons, you could theoretically input how you feel on a 1-5 scale in under a second. That's my goal; I feel like a lot of other research will become possible once I can do that.
To that end, I ordered an eZ430-Chronos watch from Texas Instruments. Now, I'd like to go play with it, but -- Windows and Linux only! (at home I only have a Mac.) D'oh. You'd think I would have checked this first. Another reason I'd like to go back to Linux. Well, I'll keep you posted if I make anything cool.