[sci.electronics] Answering Machines

Peter_Warren_Lee@cup.portal.com (07/17/90)

Being a hopeless paranoid type of person, I have a question about answering
machines that can be accessed remotely by a 1-4 digit code that you press
in on any touchtone phone...
 How do the circuits work that detect which buttons are being pressed?
Do they just check to see if the correct tone is present or do they also
check to make sure that ONLY the correct tones are present?
 For instance, would these systems be safe against someone with a seven 
tone generator that sent out all the tones at the same time that the phones
normally use for dialing?
Thanks,
                                  Pete
  Peter_Warren_Lee@cup.portal.com

dbell@cup.portal.com (David J Bell) (07/17/90)

And on a related issue:  My answering machine is around 3 or 4 years
old; still works fine, but I'm noticing a problem with "new" phone
systems. The remote functions of the a.m require a sequence of 3
tones, each sustained for the better part of a second, for it to 
respond. The latest PBX system at my wife's employer is fully
electronic, and just sends a short (~100 mSec) burst of tone when
she dials. Same situation with our (Mobira) cellular phone. Neither
of these will allow us to remotely pick up messages.

Does anyone know of a line of answering machines that will respond to
very short remote tones????

Dave      dbell@cup.portal.com

dt@yenta.alb.nm.us (David B. Thomas) (07/18/90)

My radio shack answering machine (which is a fantastic unit -- I highly
recommend r/s's telephone answerers), can respond to brief tones.

The security afforded by the secret code is not that great.
It expects *nn where nn is a two digit code you set with dials
on the back.  To hack, first press a star during the announcement.
If the machine stops and beeps, you are probably dealing
with such a machine.  For you hardcores, the beep is about 840 Hz.

The machine doesn't give you an obvious hint if you type a wrong guess,
so you might have to try 100 combinations, but you can try several per
call if you're quick, or if their message is longwinded :-)

						David

kcrudup@lotus.com (Kenny Crudup LID-A0794) (07/19/90)

In article <31823@cup.portal.com> dbell@cup.portal.com (David J Bell) writes:
>Does anyone know of a line of answering machines that will respond to
>very short remote tones????

I have a Pana KX-T2634. No problems w/PBX's, and you can do it *all* remotely.
$150, though, but Pana has less-top-of-the-line versions.

-- 
Kenneth R. Crudup, Lotus Development Corp. Contractor, NASD/QA system V
1 Rogers Street 6381D, Cambridge, MA 02142. (617) 693 4111.
Work: kcrudup@roxbury.lotus.com, Home: nubian!kenny@ima.ima.isc.com
"And if you act now, we can even get the car!"