The Good: The Garmin Vivosmart 3 is slim, very comfortable to wear, has a built-in heart-rate monitor and is fully waterproof. It's loaded with extra features, including stress-level measurements, VO2 Max readings, and a rep counter. It shows notifications from your phone. The Bad: Some of the features are a little difficult to access on the watch; the display isn't as sharp as some competing models' displays. The Bottom Line: Although it's not so intuitive to navigate, the slim and comfortable Vivosmart 3 is a very good activity tracker that's waterproof and feature-packed. Garmin's Vivosmart 3 activity tracker may not have HR in its naming scheme like its predecessors -- the Vivosmart HR and GPS-enabled Vivosmart HR+ -- but it does include a heart-monitor with 24-7 monitoring and adds new, smarter features while returning to the slimmer design and hidden display of the original Vivosmart. It's a nice improvement and very comfortable to wear, but it isn't without a few small drawbacks, the biggest of which is that it's not quite as intuitive to use as I'd have liked. At $140 (instead of $200), \u00a3130 in the UK and AU$229 in Australia, it's priced to compete with the Fitbit Alta HR and Fitbit Charge 2, and comes in two color options, black and purple, although the purple version is only available with a smaller band that won't be suitable for those with bigger wrists.What's new? Well, aside from the ultraslim design, you get higher end fitness-tracking tools such as VO2 max and fitness age, all-day stress tracking and a rep counter when pumping iron, doing push ups or pull ups.Like its predecessor, this model is waterproof and features 24-7 heart-rate monitoring. It automatically tracks activity, including steps, floors climbed, calories burned, intensity minutes, sleep and more. As part of that 24-7 monitoring, the device will measure your heart-rate variability and translate it into a stress level, then prompt you to breathe and relax when that level is elevated.Battery life is rated at up to 5 days of use between charges, which I confirmed in my testing. As with most fitness trackers, this one comes with a proprietary charging cable (it clamps onto the watch), not a standard Micro-USB cable. So lose it and you'll have to buy another one. This is the first product in the Garmin Vivo family to estimate VO2 max, a measurable indication of aerobic performance that was previously available only in higher-end Garmin running watches. Your VO2 max score translates into a fitness level, ranging from poor to superior, and it's also used to calculate your fitness age, "a relatable metric that puts a user's fitness level in terms of an age."