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2.5.4 Motion Actuation (A)

Understanding 2.5.4 Motion Actuation (A)

In a page or on a mobile device functionality that can be operated by device motion or user motion can also be operated by alternatives like buttons, links or other controls. There should be a way for disabling responding motion, unless the motion can operate in an accessible way or is essential

Why is this a problem?

This Success Criterion helps people who may be unable to perform tilting, shaking, or gesturing to use an interface - or the device may be mounted. Fixing this will ensure users can still operate all functionality by other means.

Notice how most of these following example are just about common sense alternatives to using motion to do things on a mobile device.

  • A user can’t hold and move the device to navigate content. A control exists to navigate also.
  • When inputting text - shaking a device shows a dialog where you can undo the text input. A cancel button next to the text field offers the same functionality.
  • A user can tilt a device to advance to the next or a previous page. Buttons or links are also provided to perform the same function.
  • A user can move the device to change the view of an image. A control is also available to do the same thing.

Requirements / What to do?

  • Do not use the devicemotion event to activate content functionality.
  • Ensure that alternative means of input exist when using device motion sensor input.
  • Provide a user preference to disable motion actuation.
  • Support OS features which allow the user to disable motion actuation.
  • Use the new prefers-reduced-motion CSS declaration. This will detect if the user would like to reduce animation or motion on the pages they visit.

Common mistakes

  • Functionality that can only be activated via device motion events (e.g., shaking or tilting)
  • The user is unable to disable motion actuation.
  • The author has turned off system level features which allow the user to disable motion actuation.