Motion Actuation
Functionality operated by device motion (shake, tilt) must also be operable with conventional UI controls. The motion-based input must also be disable-able to prevent accidental activation.
What it requires
WCAG 2.5.4 protects users who cannot reliably move their device — wheelchair-mounted tablets, users with hand tremor, users in fixed-mount checkout kiosks. The shake-to-undo iOS gesture is the canonical example: any app using it must provide a UI undo button as well, and let users disable shake-to-undo.
Most ecommerce sites do not use motion actuation, so this criterion typically passes by default. PWAs and custom mobile apps occasionally fail.
Common Shopify failure
Custom Shopify mobile PWA that uses device-tilt to switch between cart and account views with no on-screen button alternative. Rare but not unheard-of in custom Hydrogen + native-app hybrids.
How to fix it
Auto-fix flags motion-based event listeners (`devicemotion`, `deviceorientation`) and recommends button-equivalent UI alternatives.
Primary source: W3C — WCAG 2.1 Understanding 2.5.4