In telecommunications, a Foreign Exchange Office, or FXO, is a telephone signaling interface that receives POTS, or "plain ol telephone service". It generates the on-hook and off-hook indicators used to signal a loop closure at the FXS's end of the circuit. Analog telephone handsets, fax machines and (analogue) modems are FXO devices, though the term is rarely used except in connection with Foreign exchange service (FX).