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Method and Apparatus for Detecting an Intruder

IP.com Disclosure Number: IPCOM000115227D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 211K

Publishing Venue

IBM

Related People

Grady, P: AUTHOR [+2]

Abstract

Disclosed is a method and apparatus for detecting an intruder that has gained entry into a room during a tenant's absence. The tenant, upon return to the room's closed door, can detect that the room may harbor an intruder, using one of two different techniques.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 28% of the total text.

Method and Apparatus for Detecting an Intruder

      Disclosed is a method and apparatus for detecting an intruder
that has gained entry into a room during a tenant's absence.   The
tenant, upon return to the room's closed door, can detect that the
room may harbor an intruder, using one of two different techniques.

      The first technique (Model 1) involves visually observing the
departure, elapsed, and arrival time displayed upon the apparatus
base unit  LEDs.  The second technique (Model 2) involves RF
communication between the apparatus base unit and a remote hand unit.
The remote hand unit will provide an indication as to whether or not
the door had been opened during the tenant's absence.

      The common components of the base unit used in both models
include a battery and microprocessor and are  contained within a palm
sized case that mounts to the door frame on the inside of the room.
The edge of the  base unit facing the door contains three Reed
switches arranged linearly.  The middle Reed switch is aligned with a
magnet mounted upon the door to provide a closed loop circuit.  The
outer Reed switches maintain an open loop  circuit.  The reason for
this is to prevent an intruder from defeating a system were it to
have only 1 Reed switch, by carefully slipping a thin sheet of magnet
material between the door and door frame at the location of the Reed
switch, then subsequently opening the door with a spare key, entering
the room, then closing the door and removing the magnetic material.
If some means were available to locate the magnet on the inside of
the door with any degree of accuracy from outside the door, then the
above mentioned sheet magnet trick could be performed by the
intruder.  The base unit would not detect such trickery if only a
single closed loop Reed switch circuit were employed.  However, with
the outer Reed switches in an  open loop  circuit, a sheet magnet can
be detected by the polling microcode within the base unit if the
outer Reed switches are closed by the sheet magnet.  It would be
extremely difficult for an intruder to insert a sheet magnet through
the door and door frame to cover the middle Reed switch and not also
trip the outer Reed switches by accident.

      The model 1 base unit, in addition to the common components,
contains 4 LEDs mounted on the same edge of the base unit as the Reed
switches.  The LEDs are used to display departure, elapsed, and
arrival time in 1 second intervals, with a  5-second interval between
cycling the departure, elapsed, and arrival times.  The side of the
apparatus facing the interior of the room contains a keypad used  to
enter  the departure time.  Model 1 is depicted in Fig. 1.

      The model 2 base unit, in addition to the common components,
contains low power RF transmitter and receiver circuitry to
communicate to the remote hand unit.   The RF circuitry operates on
the 27 or 49 MHz unlicensed band  (<10,000 uV/meter ...