Compatibility Guide
The Screen Wake Lock API is useful, but it is not identical across every browser. Understanding secure context and visibility rules will save you a lot of frustration.
Wake lock normally requires a secure context. In practice, that means the live site should be served over HTTPS, while local testing is usually done through localhost. If you open a file directly from disk or from an unsecured HTTP origin, the browser may refuse the request immediately.
Chromium-based browsers are usually the most reliable place to test a tool like NoSleepScreen. Even then, support depends on the version, device, and power rules. A browser that supports wake lock on desktop may behave more cautiously on mobile.
Wake lock is usually tied to the active browsing context. If the tab is hidden, minimized, backgrounded, or suspended, the browser can release the lock. That is normal behavior. A visible timer on the page helps the user understand that the session is temporary and stateful.
Mobile devices often have stronger battery-saving behavior than desktops. Some devices may release wake lock more aggressively, especially when low power mode is enabled or when the page stops being the active foreground app.