The off-hook tone (also off-hook warning, howling tone, or howler tone) is a telephony signal for alerting a user that the

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 ...

has been left

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 ...

without use for an extended period, effectively disabling the

telephone line A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or ot ...

North America

The off-hook tone in exchanges of the

North American Numbering Plan The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the international calling ...

consists of a superposition of tones with the frequencies 1400 Hz, 2060 Hz, 2450 Hz, and 2600 hertz, played at a

cadence In Western musical theory, a cadence (Latin ''cadentia'', "a falling") is the end of a phrase in which the melody or harmony creates a sense of full or partial resolution, especially in music of the 16th century onwards.Don Michael Randel (199 ...

of on and off.Telcordia GR-506-CORE Issue 3 December 2011, ''Signaling for Analog Interfaces''
Section 17.2.8 ''Receiver-Off-Hook (ROH) Tone'' The signal is applied to the local loop by the switching system for

permanent signal Permanent signal (PS) in American telephony terminology, or permanent loop in British usage, is a condition in which a POTS line is off-hook without connection for an extended period of time.Telcordia Technologies, GR-505-CORE Issue 2, December ...

treatment to alert an end user (subscriber) of an off-hook condition of the telephone set, i.e. that the telephone handset should be placed on-hook. Before playing the signal, a certain

timeout Time-out, Time Out, or timeout may refer to: Time * Time-out (sport), in various sports, a break in play, called by a team * Television timeout, a break in sporting action so that a commercial break may be taken * Timeout (computing), an enginee ...

has to elapse, and on some systems an

intercept message An intercept message is a telephone recording informing the caller that the call cannot be completed, for any of a number of reasons ranging from local congestion, to disconnection of the destination phone, number dial errors or network trouble a ...

is announced (e.g. "If you'd like to make a call, please hang up and try again. If you need help, hang up and then dial your operator. This is a recording."). A single burst of off-hook tone is sometimes used to indicate to a party that the call is being transferred, notably at 1-800- BELL-SOUTH (800-235-5768). Some central office switches in the United States, notably older

GTD-5 EAX The GTD-5 EAX (General Telephone Digital Number 5 Electronic Automatic Exchange) is the Class 5 telephone switch, Class 5 telephone switch developed by GTE Automatic Electric Laboratories. This Digital data, digital telephone exchange, central off ...

systems, utilize a single frequency tone, 480 Hz, known as ''High Tone'' for this purpose. In either case, the tone is substantially louder than any other signal transmitted over a copper POTS circuit; loud enough to be heard across a room from an unused off-hook telephone.

HOWLER

In the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

, a warbling signal sounding rather like an alarm siren is played at steadily increasing volume to a telephone left off-hook and unused on telephone lines provided by the

BT Group BT Group plc ( trading as BT and formerly British Telecom) is a British multinational telecommunications holding company headquartered in London, England. It has operations in around 180 countries and is the largest provider of fixed-line, bro ...

and many

PABX A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...

extensions. It is sometimes referred to as a ''howler.'' In some cases it is composed of the

DTMF Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed ...

tones * and # played alternately. Telephone lines provided by

NTL NTL may refer to: Companies * NTL Incorporated and NTL Internet, later Virgin Media, communications media company ** NTL Ireland, later Virgin Media Ireland * Arqiva, UK company formerly ''NTL Broadcast'' and ''National Transcommunications L ...

Virgin Media Virgin Media is a British telecommunications company which provides telephone, television and internet services in the United Kingdom. Its headquarters are at Green Park in Reading, England. It is owned by Virgin Media O2, a 50:50 joint ventu ...

tend to use the American-style tones, including a recorded message.

References

External links

High Tone
Telephony signals {{telephony-stub

North America

HOWLER

See also

References

External links