About a year ago, hype about the coming trend of wear-able technology was reaching fever pitch. Rumours of Apple’s forthcoming Watch were growing, Google was testing its Glass headset and preparing the release of its Android Wear smartwatches, and health-tracking wristbands were judged the big trend to emerge from January’s Consumer Electronics Show.

Many entrepreneurs developing a next-generation product in a hot new market would have been delighted. But James Proud, founder and chief executive of San Francisco-based start-up Hello, felt uneasy.

The wristband Hello was developing was to be more advanced than established rivals such as Fitbit and Jawbone. “But you still had to charge it and you still had to wear it,” says Mr Proud, about the device, called simply Band. “That didn’t sit right with me for the whole 18 months we worked on it.” He decided the premise of a wearable device was “broken” because the technology was too intrusive and clunky.