On- and off-hook

On subscriber telephones the states are produced by placing the handset onto or off the hookswitch.

Placing the circuit into the off-hook state is also called seizing the line.

Off-hook originally referred to the condition that prevailed when telephones had a separate earpiece (receiver), which hung from its switchhook until the user initiated a telephone call by removing it.

When off hook the weight of the receiver no longer depresses the spring-loaded switchhook, thereby connecting the instrument to the telephone line.

This article incorporates public domain material from Federal Standard 1037C.