Maybe it depends on the access point. When I turn it off on my router there are no beacons sent. Unless you specifically probe the ssid it doesn’t announce itself. BUT granted when you make a connection the ssid does show up during the handshake. If you were watching at the exact moment of connection then it would be detectable. I suppose they could use a mass deauther device and cause new connections and detect while that is happening but they they would need to triangulate the location of said ap… Again a lot of extra equipment.