# Motion Actuation
Understanding SC 2.6.1

## In brief

Goal
  Content is not dependent on a user's ability to move a device.
What to do
  Don't rely solely on device motion to control page content.
Why it's important
  Some people cannot hold or move a device steadily.

## Intent of this Success Criterion

The intent of this success criterion is to ensure that functions triggered by moving a device (for example, shaking or tilting) or by gesturing towards the device (so that sensors like a camera can pick up and interpret the gesturing), can also be operated by more conventional user interface components.

This criterion concerns input through sensors which respond directly to motions such as gesturing towards, tilting or shaking a device. It does not cover the movement of users through space as registered by geolocation sensors or beacons, or events observed by the device other than intentional gesturing by the user. It also does not cover incidental 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, 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) because the device is on a fixed mount (perhaps a wheelchair) or due to motor impairments. Therefore, functionality offered through motion must also be available by another mechanism.

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. 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.

There is an exception where motion is essential for the function or not using motions or gestures would invalidate the activity. 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

- This Success Criterion helps people who may be unable to perform particular motions (such as tilting, shaking, or gesturing) because the device may be mounted or users may be physically unable to perform the necessary movement. This success criterion ensures that users can still operate all functionality by other means such as touch or via assistive technologies.
- Other users will benefit in situations where they are unable to move their devices.

## Examples of Success Criterion 2.6.1

- A user can choose an application setting which turns off Shake to Undo and other motion-activated features.
- After text is input in a field, shaking a device shows a dialog offering users to undo the 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 are also provided to perform the same function.
- 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.
- A user can gesture towards the device to navigate content. Controls are also available to navigate.

## Related Resources

- Detecting device orientation
- DeviceMotionEvent

## Techniques

### Sufficient

- G213
- GXXX: Supporting system level features which allow the user to disable motion actuation

## Advisory

## Failure

- F106: Failure due to inability to deactivate motion actuation
- FXXX: Failure of Success Criterion 2.5.4 due to disrupting or disabling system level features which allow the user to disable motion actuation