[bradleyjkemp]

Oh, 100% I need some more docs on the page: it's definitely not foolproof.

From my testing, it works even if the window is in the background somewhere but generally it stops working if you switch to a different tab within the same window.

You should get a popup though if you do something that causes the page to lose its Wake Lock (which works by listening to the release event: https://developer.mozilla.org/en-US/docs/Web/API/Screen_Wake...)