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Fox.com Tech Tuesday

(Fox News)

By Guy R. Briggs

Every other week or so, FOXNews.com tries to solve your most vexing technology-related problems. Send your questions to TechQuestions@foxnews.com and we'll reply to selected ones in our next installment.

I Am Serious. And Don't Call Me Shirley

Q: I live in Saint Paul, Minn. Tonight I received a phone call from the Obama campaign asking how I would be voting. I have an unlisted/unpublished phone number and am on the "Do Not Call" list.

How did the Obama campaign get my phone number? I make it a point NOT to enter my phone number on any Web site registrations, and I always ask anyone I do business with online to respect my privacy.

What else can I do to prevent random phone calls during dinner?

A: These are politicians, right? The same bunch who passed the legislation which set up the Federal Do Not Call Registry?

What are the odds that these guys would pass a law making it illegal for them to call you, hmm?

If you said, "slim-to-none," you're right. Political calls are excluded from the Federal DNC Registry. That means politicians can call you whenever and however they feel like it, even cell-phone numbers, whether or not your number is registered.

How did they get your phone number? They use automated equipment, which dials your area code, your three-digit local exchange prefix and each and every one of the 10,000 possible individual numbers within the local exchange, from 0000 to 9999, including yours.

How did they get your name? From any one of several reverse-lookup phone-number databases available.

Technically, here's how it works.

The automated equipment dials the number and then monitors voltage on the line. Voltage drops with respect to the ring voltage (which is about 50 volts) when the line is picked up. Then the equipment has to decide if it has a live human on the line, a fax/data modem, an answering machine or a disconnect.

If it's a human, the equipment transfers the call to the telemarketer and displays the name on his screen. The telemarketer hears a tone in his headset, looks at the name and says, "Hello, is the Smith residence?" or "Good evening, may I speak with Mr. Jones, please?"

Note that he never actually heard you answer — the equipment was still deciding if it had a carbon-based life form on the line. If he sounds a little addled when he first speaks, that's why.

If it's a modem of some sort, the equipment detects the high-pitch whistle tone — called the "carrier" tone — and keeps track of that fact in its memory.

It does the same thing if it "hears" the hiss of an answering machine tape, and, of course, if it hears the distinctive "doo-bee-DEEP" tone indicating a number no longer in service.

That tone, by the way, is called the SIT or "Special Information Tone" There are eight variations in all.

If the automated equipment hears the SIT disconnect on three successive calls, the number is removed from the master list. And that's its Achilles' Heel.

You can purchase a little piece of hardware called the "TeleZapper" (http://www.telezapper.com) for $39.95, which sends the SIT on every call you pick up, in order to fool/discourage telemarketers.

If you're more the do-it-yourself type, you can download a copy of the SIT from http://www.scn.org/~bk269/zapper.html#zapper and put it at the beginning of your answering machine message.

Then you can use the answering machine to screen calls. Telemarketing equipment "hears" the SIT when your message starts and moves on to the next number on the list; you pick up the calls from live humans.

Alternatively, if you don't want to explain the funny tones to legitimate callers, you can go to http://www.StopPoliticalCalls.org and register your telephone number with them. It's free.