Onhook

On-hook, or the on-hook state, is a term in telecommunications describing the idle state of a telephone or similar device when it is not in use. When a handset rests on its cradle, the hook switch is engaged, keeping the line in a non-active condition and preventing current from flowing in the local loop. In this state the device is effectively disconnected from the network for voice transmission, and features such as the ringer remain inactive until a call is initiated.

Lifting the handset switches the device to the off-hook state by actuating the hook switch, closing the circuit between the subscriber and the network. This allows current to flow, signaling equipment at the central office or private branch exchange to provide dial tone, accept user input, and establish a two-way voice channel. The off-hook state continues for the duration of a call, until the handset is returned to the cradle, at which point the circuit is opened again and the device returns to the on-hook state.

In modern networks, the terminology persists across traditional analog lines, digital PBX systems, and VoIP endpoints. The exact electrical characteristics vary by technology, but the conceptual distinction remains: on-hook denotes idle or not-in-use status; off-hook denotes active use or readiness to place or answer a call. The concept is closely associated with the mechanical hook switch, line state signaling, and user actions such as answering or ending a call.