Off-hook tone

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Off-hook tone" – news · newspapers · books · scholar · JSTOR (January 2008) (Learn how and when to remove this message)

The off-hook tone (also off-hook warning, howling tone, or howler tone) is a

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 Hz, 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

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

Listen to an off-hook tone from North America.

---

Problems playing this file? See media help.

High Tone

Listen to an older 480Hz off-hook tone.

---

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

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

•  Telephones portal

References

External links

• High Tone
• Design schematic