You don't have to look far to see a fitness tracker on someone's wrist. The devices are hugely popular. But a new study, one of the biggest and longest to date, suggests they may not help you lose weight.

When personal trainer Amanda Duerk was trying to lose her post-pregnancy baby weight she used a fitness tracker as part of her exercise routine.

"After I got to my goal weight, I stopped looking at it because I didn't need it anymore," said Duerk.

But what if you don't necessarily need to lose weight? Will a fitness tracker help improve your health?

A 2016 study tracked 800 adults for a year. Most wore Fitbits and logged between 50,000 and 70,000 steps a week. But after just six months none of them showed improvement with weight or blood pressure. And after a year 90 per cent of them stopped using their Fitbit altogether.

"Taking steps alone isn't enough to help you lose weight. You're going to have to pair that with an intense exercise regimen, and also with a healthy diet," said Julia Calderone, health editor with Consumer Reports.

While the results aren't exactly encouraging, some researchers suggest if the study focused on people who were heavier or had higher blood pressure they might see greater benefits.

But with so many options on the market, which tracker is rated the best?

Consumer Reports tested fitness trackers for step count and heart rate monitoring accuracy, water resistance and ease of use and pairing, as well as readability in both bright and low light.

After the extensive testing, the top rated trackers were the Fitbit surge for $330 and the TomTom Spark Cardio Plus music for $300. Another highly-rated tracker is the Garmin Vivosmart HR for $170.

Consumer Reports reached out to the makers of Fitbit who said, "Fitbit continues to invest in the development of new devices and innovative motivational tools and social features to further enhance user engagement and help individuals achieve their health and fitness goals."