Editor’s Note: The content for this tech tip combines information from World Wide Web Consortium’s (W3C) Web Content Accessibility Guidelines (WCAG) 2.1 Technique web page (available to the public) and the Office of Accessibility’s (OoA) role-based training pages (available to only state employees). Links are provided in this tip for the public pages. If you are a state employee, email us at MNITAccessibility@state.mn.us to receive the OoA links.

The OoA July blog post, WCAG 2.1 Addresses Needs for Users with Cognitive & Mobility Disabilities, mentions success criterion, 2.5.4 Motion Actuation. This standard ensures that functionality operated by device motion or user motion can also:

• Be operated by conventional user interface components, such as touch, and
• Motion responses can be disabled to prevent accidental actuation.

How Motion Actuation Works

Devices often have sensors that can act as inputs. These sensors allow the user to control something by simply changing the orientation or moving the device in particular ways. In other situations, web content can interpret user gestures via the camera or other sensors to actuate functions. For example, shaking the device might issue an "undo" command, or a gentle hand wave might be used to move forward or backward in a sequence of pages.

Some users with disabilities are not able to operate these device sensors (either not at all, or not precisely enough) to benefit from the sensors. Their device may be on a fixed mount (perhaps a wheelchair), or they physically are unable to move the device.

Motion actuation requires developers to ensure an alternative control scheme is ready, and either:

• has it set to always available, or
• is available by disabling the motion controls (making sure the motion control settings aren’t themselves motion-controlled).

In addition, some users may accidentally activate sensors due to tremors or other motor impairments. The user must have the ability to turn off motion actuation to prevent such accidental triggering of functions.

How to successfully incorporate motion actuation

• Check operating system settings and allow the user to disable motion detection at the system level.
• Provide conventional controls and an application setting for motion activated input.
• Support system level features which allow the user to disable motion actuation.

Examples

• Shake to undo: After text is entered in a field, shaking a device displays a dialog allowing users to undo the entry. Supporting use of the backspace key and/or providing a clear button next to the text field offers the same functionality.
• Shake to undo can be turned off in a settings page.
• Advance pages: A user can tilt a device to advance to the next or a previous page. Buttons are also provided to perform the same function.
• Interactive elements: A user can move or pan a device to change the view in an interactive photo. A control is also available to perform these same functions.
• Gestures: A user can gesture towards the device to navigate content. Controls are also available to navigate.
• Motion Activated Slider: A slider can be adjusted by tipping the device to the left and right. There are also buttons to achieve the same functionality, and a tick-box that prevents the motion from having an effect.
• Web Accessibility Initiative’s (WAI) working example of a slider with motion actuation.

Testing

For each function that is triggered by a motion sensor:

• Check if the use of a motion sensor is essential or required to make the function accessible is supported.
• Check if there is a user setting which disables the motion detection.

Resources

• WCAG 2.1 Quick Reference Guide.
• WCAG 2.1 Technique G213: Provide conventional controls and an application setting for motion activated input.
• Mozilla Developer Network (MDN) DeviceMotionEvent.
• MDN Detecting device orientation.

Note: This is the latest article in our series “WCAG 2.1 – Improving Digital Accessibility.” Missed the first installments? While on the Accessibility News web page review the feed for WCAG 2.1 in titles and/or the summary.