Does anyone know what type of outlet this is? I'm thinking it has to do with an old antenna but not sure. Found on a family member's house and they weren't sure.
It looks exactly like the interface for an ANSI 12.18 optical port (32 mm diameter), used for serial (RS232 or USB) interface between 'smart' watt-hour meter and the reader/monitor/programming device. Typical probe attaches to the port with internal magnet or two. One hole would be an LED (opto-transmitter) and other hole is photo-transistor (receiver).