Off-hook tone

Short description: Audible alert on a telephone left off-hook

The off-hook tone (also off-hook warning, howling tone, or howler tone) is a telephony signal for alerting a user that the telephone has been left off-hook without use for an extended period, effectively disabling the telephone line.

## Contents

* 1 North America
* 2 Howler
* 3 See also
* 4 References
* 5 External links

## North America

The off-hook tone in exchanges of the North American Numbering Plan consists of a superposition of tones with the frequencies 1400 Hz, 2060 Hz, 2450 Hz, and 2600 hertz, played at a cadence of 100 ms on and 100 ms off.[1] 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 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).

Example of a North American Off-hook tone

File:Offhook Tone.ogg

Listen to an off-hook tone from North America.

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Problems playing this file? See media help.

High Tone

File:Tone 480Hz.ogg

Listen to an older 480Hz off-hook tone.

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Problems playing this file? See media help.

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

## See also

## References

1. ↑ Telcordia GR-506-CORE Issue 3 December 2011, Signaling for Analog Interfaces, Section 17.2.8 Receiver-Off-Hook (ROH) Tone

## External links

* High Tone
* Design schematic

* v
* t
* e

Signaling (telecommunications)

* Dial tone
* Ringtone
* Ringing tone
* Busy signal
* Reorder tone
* Disconnect tone
* Special information tones
* Off-hook tone
* Dual-tone multi-frequency
* 2600 Hz

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