I have always wondered what the "arm band" was that they wore. I read this link Where are the 'Biggest Losers' now? - 'Biggest Loser' on TODAY
and this is what Ali says about it..
Ali watches her calorie intake and continues to wear the BodyBugg on her arm to measure her calorie burn. "I don't want to leave anything to guesswork when I have the tools not to," she said.
So I goolgled and now I know. It counts your burned calories and also tracks your calorie consumption by linking to a computer program that you enter you food intake into.