Path: utzoo!attcan!uunet!lll-winken!netsys!vector!nobody From: steves@tekgen.bv.tek.com (Steve Shellans) Newsgroups: comp.dcom.telecom Subject: Re: In use light Message-ID: Date: 10 Oct 88 20:33:04 GMT Sender: chip@vector.UUCP Lines: 23 Approved: telecom-request@vector.uucp (USENET Telecom Moderator) X-TELECOM-Digest: volume 8, issue 157, message 2 X-Submissions-To: telecom@bu-cs.bu.edu (TELECOM Digest Coordinator) X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) In article mgrant@cos.com (Michael Grant) writes: >X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) > >For $24.95, Hello-Direct makes a device called the "Privacy Device" on >Page 8 of their Fall catalog. It has an annoying "feature" though... > > "Make sure no one is listening in on your calls." > > "You're assured of privacy when the Silent Patrol is on duty on > your single-line telephone. Just plug it in between your phone and > the wall and it will let you know any time someone is listening in on I can readily understand how one of these devices would work if someone clips on a low-impedence handset (or phone) on your line. You can usually hear a drop in volume when someone picks up an extension phone, and this condition should be pretty easy to detect electronically. But suppose someone has a very high-impedence input to an amplifier, puts this across your line, and then just amplifies the signal as necessary. Can these privacy devices detect this situation, and if so, how? Steve Shellans Tektronix, Beaverton OR steves@tekgen.BV.TEK.COM