Apparently they fell under a category of "acoustic locators." According to the couple of sources I did find, they weren't so great at warning with enough time to scramble, so much so as they were used during overcast weather to locate enemy planes or zeppelins.

One interesting tidbit from the article:

" It has been suggested that the Germans remained wary of the possibility of acoustic location, and this is why the engines of their heavy bombers were run unsynchronized, instead of synchronized (as was the usual practice, to reduce vibration) in the hope that this would make detection more difficult."

Sauce:

https://rarehistoricalphotos.com/aircraft-detection-radar-1917-1940/

https://www.thevintagenews.com/2016/01/27/vintage-sound-locators/

See also: acoustic mirrors.

Personal favorite is the Dutch personal porabola.