A patent application filed by Apple three years ago and approved today illustrates a new twist on the iWatch concept: a sensor-packed strap acting as a dock which allows a range of interchangeable modules to be snapped into place.

It’s not anything we’re likely to see make it into production: the docking concept dates back to 2011, and was probably intended by Apple to house an iPod Nano, converting it into a smartwatch in a more sophisticated version of the watch-straps sold in Apple Stores since way back in 2010. But the patent does tell us two things …

First, Apple has been working on a smartwatch concept for a long time. Apple has always said that it believes in taking its time and launching a new product only when it is convinced it has everything right. While Wall Street has been impatiently demanding new product categories, Apple has been quietly working away behind the scenes on refining the idea.

Second, the focus on fitness and health has been there from the start: the patent describes the strap containing circuitry for things like a heartrate monitor and motion-sensor.

For both docking and standalone approaches, Apple describes how gestures could be used to control the device instead of taps and swipes.

The gesture might be a horizontal movement for one user input option (eg decline incoming call), and might be a vertical movement for another user input option (eg accept incoming call)

As ever, Apple patents give us few clues as to what to expect. The company that famously says no a thousand times for every yes patents everything imaginable and implements little of it. So while this will doubtless give fresh impetus to the rumor mill, don’t be surprised if the actual user-interface is a little more conventional.

We’ve heard plenty of iWatch rumors already, among them that it will come in three different models, in line with earlier suggestions of at least two different sizes, and that it will enter mass production in November. Morgan Stanley has suggested that the ecosystem and brand loyalty could see iWatch sales grow as fast as the iPhone or iPad.

As 9to5Mac has previously reported, Apple has assembled a team of health, fitness, and fashion experts to work on the project.

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