https://developer.mozilla.org/en-US/docs/Web/API/Window/vrdisplaydeactivate_event
Window: vrdisplaydeactivate event - Web APIs | MDN
The vrdisplaydeactivate event of the WebVR API is fired when a VR display can no longer be presented to, for example if an HMD has gone into standby or sleep...
event webwindowapismdn