Well, that's a good thing. The accuracy on those things is suspect, but its still important to monitor your heart rate while doing cardio. The point here is that things like hunger pains and other symptoms could indicate over-exertion. I'm a cyclist, and I never, ever go out without a heart rate monitor on because, much in the same way that a tachometer on a car is there to warn you when your over revving an engine, over-revving your heart could cause a heart attack. Have you checked what your maximum heart rate should be?