Fitbit has upgraded the smartphone Caller ID, Text and Calendar alerts, which use the Charge 2's vibration motor – adding Reminders to Move, which alerts you if you aren't moving enough during the day. Fitbit encourages you to take at least 250 steps an hour during the day. Desk-bound workers or daytime TV viewers will be egged on to get up and get moving. These hourly activity stats also show up on the mobile Fitbit app.

The Call and Calendar notifications are excellent, although the Texts on your wrist are a little slow to arrive and show only the first 40 characters, although that's usually enough. Such notifications are welcome, though – especially when exercising. Fitbit has changed the sequence for text notifications has changed. Now the message scrolls first, then the sender’s name.

The Do Not Disturb option means you now can turn notifications (calls, text, calendar alerts, reminders to move) on or off directly from your Charge 2. While in the main clock face menu on your device, you press and hold down the side button. Or click the side button until you come to the notification screen and then press and hold down that same button to turn notifications on or off.

When you’ve got more than one unread notification, a plus sign (+) appears on the tracker display.

The Charge 2 expands on the HR's multi-sport tracking capabilities, with a connection to the user's smartphone GPS for data on pace and distance. Users can track specific exercises such as running, weights or yoga to see their workout stats on the tracker's display. The lack of a built-in GPS might disappoint some runners and cyclists who prefer not to carry their smartphone with them on a run or bike ride. Apple has just added a built-in GPS to its Series 2 Apple Watch (from £369). See Fitbit vs Apple Watch for a more detailed comparison.

The Blaze and the Ionic also feature multi-sport modes and Cardio Fitness Levels, but not the Alta HR.

SmartTrack automatically recognizes select fitness activities and records them in the Exercise section of the Fitbit mobile app.

The Charge 2 lets complete a series of guided intervals during your workout. Interval training includes any workout that alternates between intense bursts of activity followed by periods of lower intensity activity or rest. Adding intervals to your workouts can help you burn more calories and improve your aerobic capacity. The tracker will vibrate and you’ll see the word “Move” on your screen when you should begin moving. When it’s time to recover, your tracker will vibrate again and you’ll see the word “Rest”.

If say you’re stuck at a traffic light during your run, you can press the tracker’s button to pause any multi-sport exercise mode. The screen will flash while your workout is on hold. When you’re ready to resume, you press the button again.

The Charge 2’s interval timer vibrates when it’s time to transition between intervals. The dimmed display screen will now also light up, making it even easier to follow along.

The Charge 2 automatically records select exercises such as hiking and cycling, so users get credit even if they forget to log a workout. Swimmers should consider the waterproof Fitbit Flex 2. Fitbit allows multiple trackers to be active on an account, so a Charge 2 user could switch to a Flex 2 when entering the pool or a watery environment. While this continues to monitor your activity we weren't overly impressed with the Flex 2's ability to accurately measure swimming activities.

Fitbit Charge 2 Cardio

Fitbit has ialso introduced a Fitbit Cardio Fitness Level that allows the user to see a snapshot of their fitness level using a personalised Cardio Fitness Score. Viewable in the heart-rate section of the Fitbit app, the score is an estimation of your VO2 Max (the maximum amount of oxygen your body can use when you’re working out at your hardest). Cardio Fitness Level issues users a rating based on their resting heart rate and personal information (such as weight) from their profile that compares their fitness against other people of the same age range and gender.

This is a much easier way to work out your VO2 Max score. Usually this is measured in a lab where you run on a treadmill or ride a stationary bike until exhaustion with a mask strapped to your nose and mouth to gauge the amount of air you inhale and exhale. You can't see your Cardio Fitness score on the tracker itself (although Fitbit has hinted that this may change with a software update). You can find it on the Fitbit mobile app.

Fitbit says that you may need to go on several runs that are at least 10 minutes in length to affect your score.

Fitbit Guided Breathing

Sometimes it's healthy to calm down. Fitbit has introduced Guided Breathing, which is meant to help users find "moments of calm" throughout the day with personalized breathing sessions based on their heart rate. This is similar to the Breathe app Apple is introducing on the Apple Watch shortly. Similarly, Fitbit's feature uses the vibration motor so you can breathe in sync without looking at the screen. There's a choice of two minutes or five minutes, and it takes around 30 seconds to measure your initial heart rate and personalise the session.

Fitbit Charge 2 hands-on review

While in Relax mode, you can now close your eyes or look away from your tracker – a light vibration signals when you need to inhale and exhale during your guided breathing sessions.

Fitbit Charge 2 Sleep Stages

Fitbit's Sleep Stages is a massive improvement on the previous measuring of "restlessness". Now you can see when you were in Deep Sleep, Light Sleep and dreamy REM Sleep, and also when you were awake during the night. You can benchmark these stages of sleep against people of a similar age.

Your sleep stages are estimated using a combination of movement and heart-rate patterns. While you’re sleeping, the Charge 2 tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between the different sleep stages. 

Fitbit Charge 2 review: display, strap, looks

The Fitbit Charge 2 features a large interactive OLED display, which shows off more fitness data right on your wrist. As well as the time and date, you also see two stats, and a simple tap on the screen toggles to the next set of information. You can personalise what you see, and choose from different clock styles via the app.

It's monochrome, and less luscious than the Apple Watch or even Fitbit's own Blaze or Ionic trackers, but this keeps the battery life longer.

Fitbit Charge 2 hands-on review

This type of display was first seen on the Fitbit Alta, with customisable watch faces. You can wear the Charge 2 as your main timepiece or double up with your favourite standard watch if you prefer. With the call, text and calendar notifications (plus the fitness tracking features) the Charge 2 will certainly offer you more than a normal wristwatch.

At first I wondered how useful this larger screen would be. I don't need to see the time and date alongside every stat, but the more I use the Charge 2 the more I appreciate the larger display over my old trusty HR. It means I have to push the button less, as just raising my wrist brings up not just the time but my step count too – no need to push or tap.

Also the Caller ID and especially the Text notification alerts are really helpful on the larger display.

But to see the wealth of exercise metrics you do need to delve deeper. You can either push the side button of the tracker or tap the screen to view tracked data. Below you can see the screen displays found by pushing the side button.

Fitbit Charge 2 button screens

Below you'll see the many faces of the Fitbit Charge 2 found by tapping the display to cycle through the stats.

Fitbit Charge 2 tap to cycle

The display is still monochrome, which is fine for most of us. If you want a colour display you need to look at the Fitbit Blaze sports watch or Ionic smartwatch.

Fitbit Charge 2 review: design

Fitbit Charge 2 interchangeable straps

One of the complaints about the older Charge HR was that you couldn't replace the wristband, so if it was damaged you had to buy a whole new tracker. Fitbit says this was the number 1 user request for improving on the older Charge HR.

Fitbit has fixed this by giving the Charge 2 interchangeable straps, so you can fit the removable tracker into different colours and versions of wristband, from the Classic through Special Edition beveled-diamond designs, to luxury leather straps.

The Charge 2 retains the HR's stainless steel watch-buckle, which is much more secure than the pop-in clasp connectors of the Fitbit Alta and new Flex 2.

The Charge 2 sits a little higher on the wrist than the old HR band, so some shirt wearers might find the cuff fits less easily over the tracker, but we didn't find this extra height overly bothersome.

Fitbit Charge 2 charging cable