TONE_DETECT()

Since 16.21.0, 18.7.0 Functions

Asynchronously detects a tone

Last reviewed 2026-04-14

TONE_DETECT(freq[,duration_ms,options])

Description

The TONE_DETECT function detects a single-frequency tone and keeps track of how many times the tone has been detected.

When reading this function (instead of writing), supply tx to get the number of times a tone has been detected in the TX direction and rx to get the number of times a tone has been detected in the RX direction.

``` title="intercept2600" same => n,Set(TONE_DETECT(2600,1000,g(got-2600,s,1))=) ; detect 2600 Hz same => n,Wait(15) same => n,NoOp(${TONE_DETECT(rx)})


``` title="dropondialtone"
same => n,Set(TONE_DETECT(0,,bg(my-hangup,s,1))=) ; disconnect a call if we hear a busy signal
same => n,Goto(somewhere-else)
same => n(myhangup),Hangup()

title="removedetector" same => n,Set(TONE_DETECT(0,,x)=) ; remove the detector from the channel

Arguments

freq required - Frequency of the tone to detect. To disable frequency detection completely (e.g. for signal detection only), specify 0 for the frequency.
duration_ms - Minimum duration of tone, in ms. Default is 500ms. Using a minimum duration under 50ms is unlikely to produce accurate results.
options
- a - Match immediately on Special Information Tones, instead of or in addition to a particular frequency.
- b - Match immediately on a busy signal, instead of or in addition to a particular frequency.
- c - Match immediately on a dial tone, instead of or in addition to a particular frequency.
- d - Custom decibel threshold to use. Default is 16.
- e - Automatically end detection after desired number of hits (as specified in the n option.
- g - Go to the specified context,exten,priority if tone is received on this channel. Detection will not end automatically, unless the e option is also specified.
- h - Go to the specified context,exten,priority if tone is transmitted on this channel. Detection will not end automatically, unless the e option is also specified.
- n - Number of times the tone should be detected (subject to the provided timeout) before going to the destination provided in the g or h option. Default is 1.
- p - Match immediately on audible ringback tone, instead of or in addition to a particular frequency.
- r - Apply to received frames only. Default is both directions.
- s - Squelch tone.
- t - Apply to transmitted frames only. Default is both directions.
- x - Destroy the detector (stop detection).

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