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[′ȯn ‚hu̇k]
The idle state (open loop) of a subscriber or PBX user loop.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


The state of a telephone line that allows dialing and transmission but prohibits incoming calls from being answered. The phone is off-hook when the handset is lifted off the base of a stationary phone or when Talk is pressed on a portable phone.

The term stems from the days when the handset rested on an actual hook. When it was removed, a spring caused contacts to press together, closing the circuit from the telephone to the switchboard in the central office (CO). When a handset is placed back on the base, it is said to be "on-hook," and the phone can receive a call. See central office.

There Really Was a Hook
The hook on this Kellogg telephone (circa 1899) was attached to a spring. When the handset was removed, the contacts inside completed the circuit between the telephone and the central office.
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The company's new On-Hook Status feature completely integrates Clearplan data, enabling lenders to be notified instantly that the repossession is complete, at no additional cost to lenders or recovery agents.
Defined by the Committee on National Security Systems (CNSS), the TSG type-acceptance program requires all telephones used in sensitive discussion areas to be physically incapable of producing any microphonic audio or intelligible video on any wires leaving the instrument while it is in an on-hook state.
"Video signal interruption by on-hook, off-hook telephone usage has plagued Triple Play delivery since the concept first became reality," explained Broadband Forum Chief Operating Officer Robin Mersh.
The Tone Commander 7810 TSG-6 IP phone is Class-A compliant and can be used in Sensitive Compartmented Information Facilities (SCIF) areas without any other equipment for on-hook security.
It prevents the telephone from being used as a passive listening device when the handset is in the on-hook position.
In our study, set duration represented the maximum possible time a given fish was "on-hook," and thus was only the coarsest of measures of the magnitude and duration of stress experienced by hooked fishes.
Features include hold, transfer, call forward, "on-hook" dialing, conference, headset support, message waiting indicator and adjustable ringer volume.
If your fax does not have a handset dial from the keypad using on-hook dialling or polling mode.
For AAL-2 signaling support, it provides generation of AAL-2 off-hook messages, detection of AAL-2 (type 1) dialtone messages and generation of AAL-2 on-hook messages.
It includes advanced features such as LCR and ADSI for cost effective electronic commerce applications ISD-T360 Features -- Crystal clear sound quality -- Full Caller-ID support (on-hook, off-hook, ADSI) for multiple countries -- Full duplex speakerphone with echo and noise cancellation -- New improved voice/music algorithm -- Selectable master/slave codec interface for maximum flexibility in chip-set integration -- A/DRAM and Flash support up to 64 Mbit -- Three and five volt support in the same chip Pricing and Availability The ISD-T360 product family is priced from $3.50 (US) - $5.00 (U.S.), depending on package and feature set, for quantities of 10,000 units.
Transmission features include one-touch autodial, redial and hold with music, customized header print, contrast control and on-hook dialing and monitoring.