South Korea's LG is among the latest to join the market with its Smart Activity Tracker - a bracelet device which resembles Nike's bestselling Fuelband.

BBC: CES 2013: Health and safety technology booms

"We believe this all-new version of our flagship activity and sleep tracker, combined with state-of-the art Bluetooth syncing and our fresh, innovative social features will create a great experience that will inspire and empower people to live healthier more active lives, " James Park, CEO and founder of Fitbit.

ENGADGET: Fitbit One tracker now ready to wake you up, count your calories all day for $100

The percentage of Tesla shares on loan a proxy for short-selling activity stands at about 25% of the shares available for trading, according to data from securities-financing tracker Markit.

WSJ: Day Traders Steer Tesla Higher