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, colloquially referred to as a phone, is a telecommunications device that enables 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 ...
has been left
off-hook 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 oth ...
.
North America
The off-hook tone in exchanges of the
North American Numbering Plan
The North American Numbering Plan (NANP) is an integrated 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, World Numbering Zone ...
consists of a superposition of tones with the frequencies 1400 Hz, 2060 Hz, 2450 Hz, and
2600 Hz, played at a
cadence 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 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 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 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 Northwestern Europe, off the coast of European mainland, the 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 and many PABX extensions. It is sometimes referred to as a ''howler.''
In some cases it is composed of the DTMF tones * and # played alternately.
Telephone lines provided by NTL/Virgin Media
Virgin Media Limited 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 ...
tend to use the American-style tones, including a recorded message.
See also
*
References
External links
High Tone
{{Telsigs
Telephony signals