When it comes to activity tracking devices, Fitbit is a name many will recognise. The company already offers a huge number of options and they have just announced two more are on their way.

There are currently eight devices in the Fitbit line-up comprising the Zip, One, Flex, Alta, Charge, Charge HR, Blaze and Surge. The Charge, Charge HR and Flex have just had their successors announced though.

Here is everything we know about the Fitbit Charge 2 and Flex 2. 

The Fitbit Charge 2 looks like a larger version of the Fitbit Alta but with the addition of heart rate monitoring and a number of other features.

Until the launch of the new devices, there were two Charge devices - the Charge and the Charge HR. They were almost identical in design, apart from the latter had Fitbit's PurePulse heart rate monitor on board, while the former didn't and they fastened differently. Both have been replaced by just one new Charge, combining the two older devices together.

The Charge 2 sports a display five times larger than the current Charge devices, allowing it to show some smartphone notifications like the Fitbit Alta, along with steps, distance travelled and the rest of the more common metrics found on an activity tracker.

The Charge 2 also has interchangeable bands, again like the Alta, allowing the user to change the elastomer strap for a different look. The standard buckle fastening found on the original Charge HR, as well as the Blaze, is still be present for the Charge 2, meaning it will feel secure on the wrist. It comes in black and silver, plum and silver, blue and silver and teal and silver as standard options but there are also lavender and rose gold or black and gunmetal special edition models.

The Flex 2 is a more simplistic and smaller device, in comparison to the Charge 2. Like the original Flex, the Flex 2 will be a plain elastomer band with LED lights to represent progress.

The original Flex had a smooth finish, while the Flex 2 has a textured finish like the Fitbit Alta. It will feature five LEDs like the original but they are positioned vertically, rather than horizontally. It will come in four colour options comprising black, lavender, magenta and navy. 

The Flex 2 uses a two-pin fastening method, like the Alta does and like the original Flex does. There will also be interchangeable accessories for the Flex 2, in the form of the Luxe collection which comprises a bangle or pendant with the bangle available in silver, gold and rose gold options, while the pendant comes in gold and silver. This follows the path of the original Flex, where the removable tracker could be placed into specially-made accessories from Tory Burch.

The Charge 2 offers PurePulse heart rate monitoring, as we mentioned above. It also offers all-day activity and sleep tracking, as the original Charge and Charge HR do, as well as Multi-Sport tracking and smartphone notifications, both of which the Alta does. Connected GPS is also on board, along with two new features called Cardio Fitness Level, which gives you a personalised fitness score over time, and Guided Breathing, which offers personalised breathing sessions based on your heart rate.

Additionally, the Charge 2 measures steps taken, distance travelled, floors climbed, calories burned, heart rate, active minutes and sleep duration, along with call, text and calendar notifications.

Sadly, there is no waterproofing capabilities for the Charge 2 so you won't be able to swim with it, but there is for the Flex 2. The Flex 2 is swim-proof, while also offering sleep quality information and all-day activity monitoring. It is the only water-resistant Fitbit tracker available. 

The Flex 2 also measures steps taken, distance travelled, calories burned, active minutes and sleep duration. There is no altimeter so it won't measure elevation but it does deliver call and text alerts in the form of colour-coded LED lights. The Flex 2 will light up blue for calls and purple for texts.

The Fitbit Charge 2 and Fitbit Flex 2 were both announced on 29 August and both are available to pre-order already through Fitbit's website.

The Fitbit Charge 2 will ship in mid-September, while the Fitbit Flex 2 will ship early October.

The Fitbit Charge 2 will start from £129.99 ($149.99). The special edition model will cost £149.99 ($169.99). The Charge 2 will come with a Classic band as standard.

Each extra Classic Band for the Charge 2 will cost £19.99 ($39.99) and there are five options. A Leather Band costs £59.99 ($79.99) and there are three options.

The Fitbit Flex 2 will cost £79.99 ($99.99). Both the Luxe Collection Bangle and Pendant start at £69.99 ($89.99).