It works only if dev tools are anchored to the page.

[fabiocaccamo]

If you just detach the dev tools from the page, it will not work anymore.

[papb]

This is known

[FranciscoG]

check out this solution. It will work no matter if it's docked or not. It uses requestAnimationFrame though but you can change it to use a less frequent setInterval like devtools-detect does.

The only downside is that it constantly pollutes the console by continually logging but for now it's the only foolproof solution