It was usually called a "cricket".
Watch the movie "The Longest Day". there's a scene in it about them, and how they were intended to be used.
One click, was to be answered by two clicks, and generally it did work, in the dark and confusion, but there is also a scene in the movie where a paratrooper gets shot after coming out in the open because he heard two clicks.
The two clicks that guy heard was a German working the bolt on his Mauser 98 rifle...
I don't think they were used after the D-Day invasion.
If you're talking about something else, you need to explain a bit more...