Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hplsla!tomb
From: tomb@hplsla.HP.COM (Tom Bruhns)
Newsgroups: sci.electronics
Subject: Re: How can I restrict outgoing phone calls? (2nd try)
Message-ID: <5170029@hplsla.HP.COM>
Date: 19 May 89 16:15:39 GMT
References: <781@tetons.UUCP>
Organization: HP Lake Stevens, WA
Lines: 55

> gnd@tetons.UUCP (Greg Darnell) writes:
>In article <1989May18.042535.9003@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes:
>> In article <21001@genrad.UUCP> cah@genrad.UUCP (Chris A. Heitmann) writes:
>> >...If you do what you say, disable the keypad, they
>> >can still make calls anywhere they want with a hand held dialer (assuming
>> >that you have tone service)...
>> 
>> And if they're deft, they can make calls anywhere they want even if you
>> *don't* have tone service, by rapidly pulsing the hookswitch (the switch
>
>I agree there are many ways to get around disabling the dialing method.
>Somebody with a Dick Tracy (Casio) phone dialing watch, or a little
>dialer, or with fast fingers, or with a computer with a modem with an 
>external speaker they hold up to the phone.  Hell, why not plug in your
>own phone if it's modular!  My point, which I should have made clear in
>the first posting, was to stop the casual phone thief, just as an auto
>or home burglar alarm may only deter the amateur burglar.  And to do
>this for less than $370 plus $5/month.  Unfortunately, our telco does
>not offer local-only service; even if you have no long distance carrier,
>in-state calls (which can be just as expensive as long distance) can 
>still be made.
>  Any new ideas?
>
>-- 
> Greg Darnell    Amdahl Corporation    143 N. 2 E., Rexburg, Idaho 83440
>  UUCP:{ames,decwrl,sun,uunet}!amdahl!tetons!gnd          (208) 356-8915
>  INTERNET: gnd@tetons.idaho.amdahl.com
>----------

Well, this is something I would like to do also (as part of a more
grandiose phone plan).  So far my thoughts lead to a project that is
probably bigger than $370, unless it could be done in volume.  If I
do it, it will be a labor of love.  But your posting got me thinking
about a simpler solution that may work for you.  Here it is:

Put a box in series with the phone line.  This box eavesdrops on the
line (perhaps through a current-sense transformer, so it doesn't have
to worry about ringing voltage so much).  If it hears a tone-pair, it
opens up the line long enough to disconnect.  It also has a set of
buttons on it that actuate an autodialer that is not listened to by
the box; the autodialer is programmed with the selected phone numbers.
It should be possible to build such a beast for a parts cost under
$50.  (It could probably even be built to extend on-hook breaks
enough that it would be impossible to dial out with hook depressions.)

You can probably think of how this could be extended to dial any
local prefix, then allow an arbitrary final four digits.  That would
complicate things considerably, I suspect, but could still be done
cheaper than $370.

Of course, it's up to you to insure this thing meets appropriate
regulations...

Tom Bruhns
tomb%hplsla@hplabs.hp.com