Motion Actuation
Two things are required together here, not one. Anything a device movement or a body gesture can do also has to be doable from ordinary controls, and the response to motion has to be switchable off so nobody triggers it by accident. Both halves, every time. The scope is wider than shaking a phone, because the rule says device motion or user motion, so gesturing at a camera that reads your hand, face or eyes is inside it too. Four things sit outside. Moving through space, the way geolocation sensors and location beacons register it. The movement of pointing a camera at a QR code or a document so it can be recognised. Anything the device notices that was not an intentional gesture. And the everyday motion of typing, clicking or touching a screen. Two exceptions finish it, covering motion that works through an accessibility supported interface, and motion that is essential, which is how a pedometer counts steps.
Why it matters
Motion input fails in both directions at the same time. A device clamped to a wheelchair cannot be shaken at all, and neither can one in a car mount or on a stand, so the feature is simply unavailable. Meanwhile a hand with a tremor produces the trigger over and over without meaning to, so the same feature fires constantly. One group cannot reach it and the other cannot escape it. A button and an off switch solve both, and the button is the part that also helps everybody holding a phone one-handed on a train.
Who this rule protects
This affects people using a device on a fixed mount, including a wheelchair mount, a car mount or a stand, people with motor impairments who cannot produce the movement precisely, people with tremors who trigger it without meaning to, and anyone whose device is not free to move at that moment.
How to check it yourself
- Find every feature the mobile experience triggers from movement, including shaking, tilting, and any gesture read through the camera.
- Check each one has a control that does the same job, meaning a button, a menu item or a link, not a keyboard shortcut.
- Check there is a way to turn motion response off, either in the site's own settings or by respecting a platform setting that disables motion detection.
- Do not count the reduced-motion preference here. It controls animation rather than input, so a site relying on it has satisfied neither half of this rule.
- Rule out what sits outside the criterion before raising a finding, meaning location, beacons, and pointing a camera at a code or a document to read it.
Failures we see most often
- A shake-to-clear-form gesture with no button anywhere that clears the form.
- Tilt-based panning in an image viewer that fires continuously for somebody with a tremor and cannot be switched off.
- A camera gesture that turns pages, with no on-screen control doing the same thing.
- A site that offers the button and no off switch. Half a conjunction is a failure, and this is usually the missing half.
Who this one is for
Read from this rule's own note above, so the grouping and the note cannot disagree.
- Motor and keyboard-onlypeople who cannot use a mouse, or cannot use one precisely
How this one is tested
We list 2 ACT rules against 2.5.4. Each one defines exactly what a checker looks at, which is how automated tools decide what to flag. Each one also checks a slice, so passing every rule here is not the same as meeting the criterion, and a rule can be proposed rather than approved or need a person to finish it. The note beside each says which.
- Device motion based changes to the content can also be created from the user interfaceA tool finds candidates, you decide
- Device motion based changes to the content can be disabledA tool finds candidates, you decide
How to fix it
- Add an ordinary control for every motion-triggered feature, and put the motion trigger behind a setting the user can switch off. Both, because the rule asks for both.
- Ask for device motion through the browser's own permission request rather than reading the sensors on sight. It puts the decision in the user's hands, and it only works over HTTPS anyway.
- Where the motion genuinely is the function, such as a step counter, that is the essential exception. Say so in the product rather than bolting on a button that does nothing useful.
Step-by-step fix guides (2)
Passes vs. fails
Passes
An Undo button sits in the toolbar, shaking still works for anyone who likes it, and a setting turns the shake off.
Fails
Undo exists only as a shake, so somebody whose phone is clamped to a wheelchair has no undo at all.
In audits and lawsuits
This is uncommon on the web and worth the two-minute check on any mobile experience, and when it does turn up it is usually a shake-to-report feature shipped in a vendor's default settings. There are two automated rules for this criterion and they split exactly along the conjunction, one for the alternative and one for the off switch, which is a useful reminder that you are testing two separate things. One correction is worth carrying because it is easy to get wrong. The reduced-motion setting is about animation and has nothing to do with an accelerometer. Honouring it does not satisfy the disable half of this rule. What does is a setting in your own interface, or support for a platform setting that turns motion detection off.