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.

unknown outlet

  • Looks like an old land-line phone jack to me.
    – Paul Logan
    Dec 6, 2017 at 6:55
  • What type of cable is coming out of the bottom. also, does it go anywhere that might indicate its use?
    – Stese
    Dec 6, 2017 at 7:11
  • What location is this (what part of the world)? Is this inside or outside the house? And @PaulLogan, I never seen a phone jack like that - where are you?
    – JPhi1618
    Dec 6, 2017 at 14:54
  • Land lines were usually 4 pin antennas were 2 pin. The cable rg57? The cable type could suggest the use also.
    – Ed Beal
    Dec 6, 2017 at 14:55
  • @JPhi168 This is in Connecticut, United States Dec 6, 2017 at 15:44

2 Answers 2


That is an optical coupler from a utility meter to allow a meter reader to electronically read the meter with a handheld data collection device. They are usually on the meter itself, but in this case the meter must be inconvenient to access so a remote coupler was used.


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).

Link: to photo of one on Amazon

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