Understanding Success Criterion 2.5.4: Motion Actuation

Functionality that can be operated by device motion or user motion can also be operated by user interface components and responding to the motion can be disabled to prevent accidental actuation, except when:

Supported Interface
The motion is used to operate functionality through an accessibility supported interface;
Essential
The motion is essential for the function and doing so would invalidate the activity.

Intent of Success Criterion 2.5.4: Motion Actuation

The intent of this success criterion is to ensure that functions that are triggered by moving a device (for example, shaking or tilting) or by gesturing towards the device so that sensors or the camera can pick up and interpret these gestures, can also be operated via user interface components, unless the motion is essential for the function and not using it would invalidate the activity.

Note: This criterion concerns input through sensors which respond directly to motions such as gesturing towards, tilting or shaking a device. It is not intended to cover the motion of users through space as registered by geolocation sensors or beacons, or events observed by the device other than intentional gestures by the user. It also does not cover indirect motion associated with operating a keyboard, pointer, or assistive technology.

Devices often have sensors that can act as inputs, such as accelerometer and gyroscope sensors on a phone or tablet device. These sensors can 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, 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) because the device is affixed to a wheelchair or due to motor impairments. Functionality must therefore be implemented in a way that other means are available to activate the function that do not rely on sensor input.

In addition, some users may accidentally active 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. Applications may be able to meet this requirement by supporting operating system settings which allow the user to disable motion detection at the system level.

Some applications are specifically created to use device sensor data. Examples of content that are exempt from this requirement include a pedometer that relies on device motion to count steps.

Benefits of Success Criterion 2.5.4: Motion Actuation

Examples of Success Criterion 2.5.4: Motion Actuation

Resources Success Criterion 2.5.4: Motion Actuation

None

Techniques for Success Criterion 2.5.4: Motion Actuation

Sufficient Techniques

  • GXXX: Do not use the devicemotion event to activate content functionality
  • GXXX: Ensure that alternative means of input exist when using device motion sensor input to activate content functionality

Advisory Techniques

Failures

  • FXXX: Content functionality can only be activated via input from devicemotion events (e.g. shaking or tilting)