Fitbit has updated its iOS app with a new feature called MobileTrack, which promises basic activity tracking on iPhone 5S even if you dont currently own a Fitbit device. For Fitbit, direct on-device tracking serves as a powerful counterpunch to other iOS fitness apps that require no extra hardware. Its also an enticing way to bring new customers into the Fitbit ecosystem; Nike has adopted a similar strategy with the launch of Nike+ Move for iOS.