Fitbit Flex 2 goes underwater (pictures)

The Fitbit Flex 2 is Fitbit's super-slim new tracker. It replaces the older Fitbit Flex.

The Flex 2 is 30 percent smaller than the old Flex tracker.

From a distance, it looks like a Jawbone Up band.

The Flex 2 pops out of its band accessories: the actual tracker is really small.

It's fully swim and shower proof, up to 50 meters. It tracks swimming and laps automatically, too.

The bands come in several colors and sizes. These are rubber, but there are optional metal bangles and pendants, too.

One of the new Fitbit-made metal bangles for the Flex 2. It opens up like a cage and holds the tracker, while the lights shine through.

The Flex 2 has a row of LED lights in several colors to show different notifications from your phone, color-coded. It also vibrates.

Other accessories will be available from Simply Vera: including Vera Wang, Tory Burch and Public School (not seen here: these are Fitbit's accessories).

The bangle comes in several sizes.

The Flex 2 can automatically track workouts or exercises.

Battery life lasts around five days.

The Flex 2 next to the new Charge 2, on the right. The Flex 2 is definitely a lot smaller.

Flex 2 can track steps, activity and sleep, but lacks a heart-rate tracker.

It also doesn't have a true display, so it can't work as a watch.

It's light enough to feel invisible.

Hopefully Fitbit will make its other trackers waterproof someday, too.

CNET senior editor Bridget Carey said she liked the look of the Flex 2 pendant.

But she complained the bangle "lacked pizzazz"

Here's some more shots of the Flex 2 inside of the accessory pendant.

It comes in both gold and silver.

You can even see the LED lights through the casing.

The Flex 2 cost $100 (£80 UK, or AU$150), which makes it pretty compelling, if you're looking for a basic slim tracker.