The Up2 is slimmer, and has a one-size-fits-all design.

The Up2 tracks steps, activity and sleep, but not heart rate. It has a battery life that lasts 7 days.

The Up2 vibrates and has a few LEDs to let you know it's on, but no display: you have to check your phone for fitness stats and coaching.

It looks good, and pretty low-key. It'll be available in grey and black, for now.

The top metal part of the band activates by tapping it, so you can switch to sleep-tracking mode (it recognizes sleep patterns automatically as you use it).

The Jawbone Up3 looks just like the Up2, and is the same size. But, it tracks heart rate.

It uses bioimpedance to measure heart rate, not LED-based tech like other bands: it can measure temperature and galvanic skin response, too, much like the Basis watches.

A look at the underside of Up3, and its magnetic charging port: it comes with a bendable USB dongle.

A new metal clasp adjusts to all wrist sizes, but it's hard to attach easily.

The Up3 will also come in two colors, black and grey. It costs $180, more than the previous Up24.

The Up3 is shower-friendly, but can't be worn while swimming. It lasts 7 days on a battery charge. And its heart rate tracking measures resting heart rate, incorporating the results in sleep analysis.

Can the Jawbone Up3 offer superior heart rate tracking? Stay tuned for a review.