[LisaS]

back to the original question - I think both use accelerometers to gauge your activity. This is good for walking/running and overall activity (compared to just a step counter). Not as good for cycling - but you still get the HR measure. the bodybug also includes HR & skin measures (e.g. sweat) AFAIK. I'm not sure how/if the 2nd does HR other than the version that specifically includes HRM. and of course whatever software and proprietary algorithms are used to translate the measures into "calories burned" would also be a difference in the products, as well as displays and reporting available.