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From: fish@ihu1g.UUCP (Bob Fishell)
Newsgroups: net.consumers
Subject: Re: How to turn off junk phone calls.
Message-ID: <325@ihu1g.UUCP>
Date: Fri, 4-May-84 14:58:14 EDT
Article-I.D.: ihu1g.325
Posted: Fri May  4 14:58:14 1984
Date-Received: Sat, 5-May-84 01:35:09 EDT
References: <366@cyb-eng.UUCP>
Organization: AT&T Bell Labs, Naperville, IL
Lines: 32

The current issue of "Radio-Electronics" has a construction article
which describes a black box you can hook up to your phone system
which will reject calls made by anybody who doesn't know a code.
I haven't read the whole article in detail, but it apparently,

1) disables the ringer, or maybe the whole phone,

2) answers the phone when it "rings"

3) listens for a touch-tone digit (the article's instructions specify
   '7')

4) if the digit is received, it will ring, otherwise, it won't.

This seems like a handy gadget to have, but there are some obvious
flaws with it. First of all, you have to tell all of your friends
about the code.  Secondly, it only works if your friend has a
touch-tone phone.  Finally, anybody calling collect (as in an
emergency) is out of luck.  Furthermore, a single-digit code
would sooner or later be cracked by anybody wise enough to do
a little experimenting if the use of these devices ever becomes
well-known.  If I build one, I think I'll program it for a
three or four digit sequence, and build in some kind of bypass
mechanism, say, a 60-second timer, to allow for people who really
have to get through, but don't have a touch-tone phone.  Any salesman
nervy enough to wait that long would be well deserving of the invective
that would follow my answering an 'emergency' call.

-- 

                               Bob Fishell
                               ihnp4!ihu1g!fish