Wednesday, July 22, 2009


How-to ZAP Telemarketers

If you're like me you're sick and tired of those annoying telemarkters, Perhaps you've heard of a neat little tool called the TeleZapper.

The TeleZapper promises to help reduce or eliminate your telemarketing calls, you install it in serial with your phone. When you recieve a call, the TeleZapper waits for you to pick up the phone, and then sends this tone [telezap.wav]. You may have heard this tone before if you've ever dialed a number that is no longer in service.

The predictive dialing tool upon hearing this tool normally removes your number from its database (Though it doesn't have to)

If you want to try it for yourself, you can download the tone and play it just before your answering machine greeting. Theoretically this should work the same way, when you see a telemarkter call you; just let your answering machine pick up. Of course non telemarkters will hear this tone too, which may be somewhat annoying.

You can also use some free windows software tools which will do a similar thing.

Related Links:

How to get even with Telemarkters (
Wikipedia Predictive Dialers (
Canada Do Not Call List (
Buy the Telezapper

Technical Details:

At my house, I use a linux (Ubuntu) OS. I use the package called "vgetty" to monitor my incoming phone calls. When the little script I wrote detects a possible telemarkter (by caller id). It sends the disconnected tone, to the autodialer.

In theory, this should cause these companies to remove my name from the list (assuming they respect the tone, and that I generated the tone correctly).

I will be monitoring this system over the next few months to see if it actually reduces any calls (are the call systems removing me from their lists?)

Even more technical "geeky" details:

My voice modem is a TOPIC (FM56PCI-TP) modem. This modem does not really work well with vgetty. It detects it as a multitech modem. The Multitech modem does not use the same compression mode as my modem, and although it plays the sound there is a large screetcy noise.

It took me quite a while to figure out how to fix this. In the end, it was necessary to force the vgetty (vm) software to detect my modem as a standard V253 modem. However, my modem uses a different flow control AT command and a different command to set the compression rate.

To fix this I had to edit the vgetty/mgetty source specifically the voicelib/ file and replace the commands.

If you want to play around with this.

Here is the "diff" of the changes I made V253modem.diff
Here is the perl script I use to play the greeting
Here is the zap (wave) file (Remember: you have to convert it to an rmdfile). To do this you can follow thie instructions here:

Telezap Wav file courtsy of:

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