Guibord Technical Writing Services, Inc.



How to get rid of telemarketers
even if they spoof the telephone number from which they are calling

2016 © Guibord Technical Writing Services, Inc.



This article was updated on December 15, 2016




Information on Caller ID spoofing




First, get your telephone service provider’s call privacy service. It allows only identified callers to connect to your telephone number. Callers with a private or unknown phone number are asked to identify themselves before the call is allowed to go through.



Calls from telemarketers who do not spoof their telephone number

Get a call blocker. Google > call blocker. Read reviews about the product you plan on buying. You can usually get it from Amazon, eBay and other online stores. Make sure that the call blocker you are buying has a caller ID display, unless your telephone set has one.



Calls from telemarketers who spoof their telephone number

NOTE: There is a device on the market that does the same as the setup described in this article. It is called a TeleZapper.

Google > telezapper. Read reviews about the product; e.g., on
Since the introduction of the TeleZapper, some telemarketers have set their robo-callers to ignore the no telephone service tone described in this article. So some telemarketers may persist calling you.





You need the call blocker previously described.


To get rid of telemarketers who spoof their telephone number, you need to send them the tone that precedes the usual “There is no service for the number you have dialed” message, or other similar message issued by your telephone service provider for out of service numbers. The no telephone service tone (hereinafter simply tone) must be the first audio signal the telemarketers’ robots hear.


Here is that tone and its file: no_telephone_service_tone.wav


Calling robots used by telemarketers monitor for that tone. If it is the first audio signal they hear when the number they are calling answers, they hang up, register that number as a number not to call and then dial another number on their call list.


Figure 1 illustrates how to get the “There is no service for the number you have dialed” tone on your telephone line as the very first tone before you answer a telemarketer spoofing the telephone number from which calls are made.



Anti-telemarketer telephone and audio tone setup



Figure 1 — Anti-telemarketers telephone and audio tone setup



The illustrated Telephone Line Voice Recorder Adapter is a device designed and engineered as an interface for telephone call recording. It transmits telephone audio signals to a tape recorder. But you can also use it to send a tone on a telephone line; essentially because it uses a small audio transformer that transmits audio signals to/from the telephone line. The audio transformer also serves as an electrical insulator between the telephone line and the audio line.


These devices can usually be purchased for around $10 on Amazon or eBay. The telephone line voice recorder adapter used for this setup was purchased on > Telephone Line Call Recorder. It comes supplied with an audio cable (equipped with a 3.5 mm plug at each end) and a telephone cable. Other brands and models also work. If uncertain, please do not hesitate to email me: . As time goes by, readers of this article will find compatible telephone line voice recorder adapters. They will be listed in this list of compatible telephone line voice recorder adapters.

Telephone line voice recorder adapter

Figure 2 — Telephone line voice recorder adapter



To send the tone on the telephone line when a telemarketer calls, you need to automate the sending of the tone with the simple pressing of a key, say as an example F2 on your keyboard. To do that, download AutoHotkey and install it on the PC or laptop that you will be using to send the tone.


Once installed, download and place the following file in Windows’ startup folder: anti-telemarketers.ahk (right click on the link, then use "Save link as..."). This file automates playing the tone when the F2 key is pressed.



Anti-Telemarketers.ahk file in Windows startup folder



Figure 3 — anti-telemarketers.ahk file in Windows’ startup folder



To edit the ahk file, right click on it and choose Edit Script. Check that the anti-telemarketers.ahk file contains only the following code:




SendMode Input

SetWorkingDir %A_ScriptDir%




; Control::




Run, C:\no_telephone_service_tone.wav




; Recommended for performance and compatibility with future AutoHotkey releases.

; Enable warnings to assist with detecting common errors.

; Recommended for new scripts due to its superior speed and reliability.

; Ensures a consistent starting directory.


; Hotkey is F2


; If you prefer to use the Control (Ctrl) key as a hotkey, put a semicolon followed

; by a space at the beginning of the F2 line, and remove the semicolon at the beginning of the

; Control line.


; Run tone file at its location on hard disk C.

; End script.


Download and place the no_telephone_service_tone.wav file in the root directory of your C drive



TIP: When you first login to Windows, it usually takes a few minutes to become fully operational. Moreover, the first time you press F2, there is usually a 2-4 seconds delay for Windows to locate the ahk and wav files and a suitable audio player. To avoid any delay for Windows to play the tone when you will receive a telemarketer’s call, press F2 once you have logged on to Windows. The next time you will press F2, the tone will be played without any delay by Windows. You must be logged on to Windows to use this method as described.


Telemarketers who spoof their number usually call while spoofing a same area code and telephone exchange, say as an example: (514) 334‑XXXX. They simply change the last four digits each time they call a string of telephone numbers. So be on the watch for these first 6 digits. Whenever you will receive a call having the first 6 digits you previously identified as originating from telemarketers, pick up the telephone handset and as you are lifting it press F2, then answer as you normally do. If it was a telemarketer, their calling robot will have heard the tone, listed your number as a no service number and stop calling you. If the calling number was not from a telemarketer, your calling party will recognize you.