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The TeleZapper is a device designed to reduce the number of telemarketing-related phone calls a household receives by imitating the tone signal normally played by a phone company to indicate a line has been disconnected. The Telezapper was created by Privacy Technologies, Inc, a wholly owned subsidiary of Royal Appliance Mfg. Co.


Telemarketing companies typically use predictive dialers to place many calls at one time. When this equipment detects that someone has answered one of the many calls it has made, it quickly transfers that call to an available agent. Calls which don't answer or numbers that are disconnected are not transferred to agents and the call is terminated automatically.

In this way, the agent is spared the time of dialing a call and waiting for an answer, and can simply speak to waiting calls which have been already set up. Additionally, if a number is determined to be disconnected, the equipment will usually mark that number as such and will not dial it again or as often.

How it works[edit]

The TeleZapper is an appliance which plugs into a consumer telephone line. On detecting a ring and answer of any phone on the line, the Telezapper will immediately play a Special information tone or 'SIT': one of eight internationally standardized signals which indicate a call cannot be completed. Typically the 'Intercept' or 'IC' SIT is used, which indicates the number called has been disconnected or changed.

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Intercept tone played by The TeleZapper (2 times)

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By playing this tone signal on the line, a predictive dialer calling the household would hear it, assume the number was disconnected, terminate the call and likely mark the number as 'disconnected' in its database.

This "tricking" of the telemarketer's equipment was effectively highlighted in marketing material for the TeleZapper as a way to get back at the "obnoxious telemarketers." The device is powered by a CR2032 battery which is not documented in the manual and is replaced by fully opening the unit.

Limitations of the TeleZapper[edit]

Because a predictive dialer merely checks for three conditions:

Some telemarketing firms have turned off the SIT tone detector altogether in response to the TeleZapper trick, rendering it wholly ineffective.

Another limitation is that the device does not work well with voice mail systems. This is because voice mail reroutes the call from a physical line to the voice mail service without the phone ever picking up.

External links[edit]