Forbes FYI for Oct05 had a quick product overview of a small device called StressEraser that retails for $400 (seems pretty expensive, I think that MAKE magazine should come up with a cheaper alternative).

The unit apparently monitors your "blood" pressure via you index finger, and then gauges your stress level.  If your level is too high, then it attempts to get you to use breathing techniques to get you back to a better emotional focus level.