Dan Adams, a sales executive from Ogden, Utah, entered a friendly contest with two co-workers to see who could take the most steps in a week. With five hours to go, he was trailing.

So Mr. Adams taped his Fitbit activity tracker to the blade of an electric saw and left it vibrating on a work bench. When he returned early the next morning, the saw’s vibrations had registered 57,000 steps.

Mr....