Fitness band maker Fitbit lost money in 2017 after selling fewer devices during the year, as it warned over shifting consumer tastes.
The results prompted shares in Fitbit to slip as much as 14 per cent in after-hours trading. The company has lost more than 80pc of its value since floating in 2015.
Fitbit said it sold 15.3 million devices last year, down from 22.3 million devices in 2016, though the average selling prices of those devices was 8 per cent higher last year at US$101 ($139) per device.
In the crucial festive quarter, ended December 31, it sold 5.4 million devices, down from 6.5 million the same period last year.
Its revenue for the year as a whole fell to US$1.62 billion from $2.17 billion, and its net loss widened to US$277.2 million from US$102.8m. Meanwhile, its cash, cash equivalents, and marketable securities came in at US$679m at the end of the year, down from US$706m a year earlier.
The group said it expected a 15 per cent to 20 per cent drop in revenue for the current quarter, to the end of March, given "consumer demand shifting towards smartwatches", meaning it expects to generate revenue of between US$240m and US$255m for the quarter. This is well below the US$340m analysts had been expecting prior to this week's results.
Fitbit's concerns over the competition follows a research note from CCS Insight last week, which forecast that demand for smartwatches would soar over the next five years, with sales expected to come in at around 71 million this year and then rise to 140 million by 2022.
Apple is perhaps Fitbit's toughest competition, with sales of the Apple Watch last year topping 18 million, more than 50 per cent more than in 2016.
Ben Wood, the director of research at CCS, said: "The bottom line is that Apple is completely dominating the market in terms of volume and value and Fitbit must be concerned by Apple's increasing focus on health and fitness."
James Park, the co-founder and chief executive of Fitbit, said: "In 2018 we'll focus on managing down expenses, continuing to expand in the smartwatch category and supporting our engaged global community on their health and fitness journeys."