Here's how it works: Given that more than 90 percent of telemarketing calls are placed with computer assistance, when either you or your answering machine answers the phone, the Telezapper emits a special tone that tells the computer your number has been permanently disconnected. Telemarketing companies that use automated dialing systems typically remove disconnected numbers from their calling lists, and as your phone number is eliminated from more and more telemarketing lists, you'll notice fewer calls. Of course, not all telemarketers use predictive dialing systems, and those that do will undoubtedly continue their work to evade the Telezapper, but it can be a partial solution.

Most predictive dialing systems will be fooled by the Telezapper's standard single tone. However, for newer dialing systems (presumably designed in response to the success of the previous Telezapper model), the TZ 900 offers an advance three-tone mode. To change the mode, unscrew and remove the protective case and then slide a recessed switch. (We suggest that Privacy Technologies put the switch on the outside for their next model.)

For the most part, regular callers are unaffected by the Telezapper, but it may "zap" calls from other organizations that use the same predictive dialing technology (such as charities, pollsters, and automated emergency weather systems) and from callers who use certain types of calling cards. (For more information, click FAQ, or frequently asked questions, in the left navigation bar.)

Installation takes seconds. Just plug the Telezapper into your phone line and your phone into the Telezapper. It's that simple. A built-in lithium-ion battery provides power and will likely last for the lifetime of the unit. The Telezapper includes a phone cord and instructions. Privacy Technologies backs the device with a one-year warranty. --Mike Brown

Pros

• Reduces telemarketing calls placed by predictive dialing systems
• Doesn't interfere with most normal calls
• Inexpensive, one-time-cost solution
• Extremely easy to install and use

• May "zap" some desired calls
• Annoying beep every time the receiver is lifted