You need to know your tool and make sure you have normal meter with you as well.
This become a bit too sensitive but I have make my own way how to use it.
The way how it works : nearer to the source it beeps more intensively . You can be 30cm from the switch and it will start beeping. But when close beeps intensify.
When no power source in your area is quiet.
Always rely on some know prove tester or read safe isolation tips .