A telephone hook or switchhook is an electrical switch which indicates when the phone is hung up, often with a lever or magnetic button inside the cradle or base where a

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

handset resides. It takes its name from old wooden wall telephones and

candlestick telephone The candlestick telephone (or pole telephone) is a style of telephone that was common from the late 1890s to the 1940s. A candlestick telephone is also often referred to as a desk stand, an upright, or a stick phone. Candlestick telephones feature ...

s, where the mouthpiece was mounted on the telephone box and, due to

sidetone Sidetone is audible feedback to someone speaking or otherwise producing sound as an indication of active transmission. Sidetone is introduced by some communications circuits and anti-sidetone circuitry is used to control its level. Sidetone is exp ...

considerations, the receiver was separate, on a cable. When the telephone was not in use, the receiver was hung on a spring-loaded hook; its weight would cause the hook to swing down and open an electrical contact, disconnecting something, but not the telephone from the line or the phone could not ring. When the handset is on the cradle, the telephone is said to be "

on-hook In telephony, on-hook and off-hook are two states of a communication circuit. 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 th ...

", or ready for a call. When the handset is off the cradle, the telephone is said to be "

off-hook In telephony, on-hook and off-hook are two states of a communication circuit. 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 th ...

", or unable to receive any (further) calls. Pushing the switchhook quickly is termed a "

hook flash On analog telephone lines with special services, a flash or register-recall signal is used to control functions on the public telephone exchange, PBX or VoIP ATA. The term "register-recall" in Europe refers to sending a discrete signal to alert t ...

Purpose

Telephone switchhook separates calling and transmitting circuits of the telephone and closes the battery circuit of transmitter to avoid a waste of battery energy. Before an invention of the switchhook the user had to manually turn the switch. Some users found that task too difficult, some forgot to turn the switch.

Invention

Several people claimed to be the first inventors of the switchhook (such as Thomas A. Watson), but

Hilborne Roosevelt Hilborne Lewis Roosevelt (December 21, 1849 – December 30, 1886) was a pioneering organ builder, telecommunication engineer, and a member of the Roosevelt family. Life Roosevelt was born in New York City to Silas Weir Roosevelt, a son of Cornel ...

managed to get recognition and royalties for his invention. The son of Edwin Holmes claimed to use that device long before their patents.

References

{{Reflist Telephony equipment Telephony signals

Purpose

Invention

See also

References