Apple invents wrist gesture input mechanism for Apple Watch
Building on a related Apple Watch patent application filed for on Thursday, Apple published an invention covering a unique wristband mechanism capable of detected wrist gestures and translating them into system inputs.

Source: USPTO
As published by the U.S. Patent and Trademark Office, Apple's patent application for "Wristband device input using wrist movement" details a method by which wrist articulations are detected and interpreted to control a wrist-worn device or a separate host device.
In some embodiments, the invention calls for a wristband that incorporates one or more sensors capable of detecting changes in the position of a user's wrist. For example, force sensors might be deployed to perceive deformation of the wristband created by forces or pressure applied as a user moves their wrist or hand.
Signals generated at the band are sent off for analysis to identify a specific wrist gesture, which is subsequently compared against a library of stored gestures mapped to certain system commands.

In practice, the wristband might measure specific levels of flexion and extension that denote a user is articulating their hand to make a "telephone" gesture, that is a hand signal with thumb and pinky finger extended. If so programmed, this particular gesture could trigger a command to answer a phone call or open a phone app on a host device. Additional gestures might control music playback volume, track selection, UI navigation, return to home and other system processes. Alternatively, gestures can be used to remotely control a wirelessly connected device, like a host iPhone.
The document goes on to detail suitable wristband materials, gesture examples, ideal sensor arrangements and other minutiae.

It is unknown whether Apple intends to build a gesture-based control system into Apple Watch, though the company is rumored to be working on active band accessories that connect to the device through its diagnostics port. Previous patent filings provide evidence of ongoing development into such solutions, including modular designs with GPS receivers and extended battery packs to full-wrist displays.
Apple's wrist gesture patent application was first filed for in April 2016 and credits Anton M. Davydov as its inventor.

Source: USPTO
As published by the U.S. Patent and Trademark Office, Apple's patent application for "Wristband device input using wrist movement" details a method by which wrist articulations are detected and interpreted to control a wrist-worn device or a separate host device.
In some embodiments, the invention calls for a wristband that incorporates one or more sensors capable of detecting changes in the position of a user's wrist. For example, force sensors might be deployed to perceive deformation of the wristband created by forces or pressure applied as a user moves their wrist or hand.
Signals generated at the band are sent off for analysis to identify a specific wrist gesture, which is subsequently compared against a library of stored gestures mapped to certain system commands.

In practice, the wristband might measure specific levels of flexion and extension that denote a user is articulating their hand to make a "telephone" gesture, that is a hand signal with thumb and pinky finger extended. If so programmed, this particular gesture could trigger a command to answer a phone call or open a phone app on a host device. Additional gestures might control music playback volume, track selection, UI navigation, return to home and other system processes. Alternatively, gestures can be used to remotely control a wirelessly connected device, like a host iPhone.
The document goes on to detail suitable wristband materials, gesture examples, ideal sensor arrangements and other minutiae.

It is unknown whether Apple intends to build a gesture-based control system into Apple Watch, though the company is rumored to be working on active band accessories that connect to the device through its diagnostics port. Previous patent filings provide evidence of ongoing development into such solutions, including modular designs with GPS receivers and extended battery packs to full-wrist displays.
Apple's wrist gesture patent application was first filed for in April 2016 and credits Anton M. Davydov as its inventor.
Comments
With a couple more accelerometers you could map many more gestures involving your arms, speed of gesture and general movement.
It's probably not that simple.