(Pocket-lint) - Fitbit promised the world it would introduce new devices this year. It's now unveiling two of them.

The new Fitbit Charge 2 and Fitbit Flex 2 are activity-tracking wristbands. They are update models, actually. For instance, much like its predecessor, the Flex 2 is a slim wearable that can track everything from your steps to calories burned. It can also measure your distance travelled and sleep. However, instead of a display, you'll get alerts via four colour-coded LED lights complemented with notifications sent to your smartphone.

Although it doesn't have an optical heart rate sensor or GPS, it comes with Fitbit's Smart Track feature, allowing the low-cost wristband to auto-detect when you've started an exercise and vibrate when you've sat still for too long. It is also Fitbit's first activity tracker to come with waterproofing - up to 50 meters, in fact. It can even detect when you're swimming. Oh, and its battery life is about five days.

As for the new Charge 2 activity tracker, it is the successor to the Charge HR. The display is about four times larger, and you must press a physical button to navigate through most options like steps, heart rate, exercise, stopwatch, etc. It comes with "connected GPS", which means if your phone is connected, it can do location tracking, accurately measure distances, and later, map your exercises in the Fitbit mobile app.

The heart-rate-sensor-equipped Charge 2 can also use your basic information like age, gender, weight, and heart levels during an exercise to serve up a cardio score metric. There's 2- or 5-minute breathing activities you can access, too. If any of this interests you, the Charge 2 costs the same price as the Charge HR ($149). Preorders are now open, with shipments beginning in mid-September.

Like the Flex 2, expected battery life is five days, Fitbit said. Speaking of the Flex 2, that wearable is cheaper ($99) than the Charge 2, naturally, and it's actually a tiny module that slots into a flexible wristband, though it can uniquely become a gold, silver, or 22-carat bracelet (sold separately) for fancier occasions. It's also now available for preorder, but it won't ship until early October.


Fitbit Charge 2 review: Taking charge

Fitbit Flex 2 review: Simple, stylish tracking

Writing by Elyse Betters.