Improvements in Electric Burglar Alarms.
Year: 1892

page_text: Date of Application, 25th Feb., 1892-Accepted, 9th July, 1892
COMPLETE SPECIFICATION.
Improvements in Electric Burglar Alarms.
I, ERNST RICHTER of Muskau in the Kingdom of Prussia and German Empire,
Tutor, do hereby declare the nature of this invention, and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement :-
The present invention relates to an electric alarm apparatus designed to give an
audible warning when doors or windows are opened, or other act of a similar
character is done by any unauthorised person. The alarm is given by the apparatus
upon the breaking or movement of a thread or cord which has been drawn across
or connected with the door window or other part sought to be protected, the thread
or cord being preferably hidden when possible.
I will describe my invention with reference to the accompanying drawings, in
which,
Figure 1 is an elevation of the circuit closing part of the apparatus enclosed
in its casing;
Figure 2, a perspective view of the same part of the apparatus with the outer
casing removed;
Figure 3, a plan ; and
Figure 4, a vertical section of Figure 1.
Figure 5 is a diagrammatic view of an application of the apparatus.
The essential part of the apparatus consists of a base A constructed of wood or
other suitable non-conducting material upon which the spring B and limb C are
fixed, (see Figures 2 and 4), by means of the plates a d. The spring is soldered
or otherwise firmly secured to the metal plate a, which may be fixed to the base
by two wood screws. It is constructed of steel and carries near its upper end a
plate b, preferably of German silver, secured to the spring by rivets and having two
lugs or projections 6 and 6" in which are secured the contact points e c¹.
The contact limb C may be constructed of German silver, and is soldered or
similarly secured to the plate d, which is fixed to the base by wood screws or
otherwise. This limb is grooved or concave, with its concavity towards the
spring B. At the points on the limb C where the contact points c c¹ come into
contact with it, it is preferred to secure contact pieces e e¹.
The plates a d are provided with terminal screws a' d¹ to which the conducting
wires may be secured in the usual manner.
When the apparatus is at rest, the spring B and the limb C are kept apart by
means of a ball K which is constructed of any suitable insulating material such as
ivory indiarubber or ebonite. (See Figure 4.) This ball is loosely held in the
position shewn by means of a thread or cord F which passes upward through the
cover plate P, and the loop O which is soldered or secured to the plate P. The
thread or cord F is either drawn past the door or window or other part to be
protected, in which case its other end is secured to the wall or a fixture, or it may
be directly connected with the part the movement of which by an unauthorised
person is desired to create an alarm. If the thread or cord has to pass around
angles or corners, it may be guided over grooved pulleys.
The conductors G G¹ lead from the terminals a' d' through the holes y y' in
the base A, to the battery and to the electric bell or alarm included in its circuit.
To protect the apparatus from dust and damp, it may be provided with a mantle
or casing G such as that shewn in Figures 1, 3, and 4, upon the upper part of
which a cover D' may be secured.
In its normal position, the ball K is in the position shewn in Figure 4, where it
separates the spring B and its contact points c c from the limb C and its contact

page_text: pieces e e¹. The elastic circuit is consequently open, and no current passes. If,
however, the thread or cord F is broken or moved in any direction, the ball K will
be lifted or allowed to fall, and the contact points c c will, by the release of the
spring B, be brought into connection with the contact pieces e e', whereupon the
electric circuit is closed and the bell or other alarm is sounded. The thread or
cord F is also so arranged that the opening of the door or window, or whatever act
or movement is desired to cause an alarm to be sounded, will either pull break or
release it, in either of which circumstances the electric current will be closed as
already described.
For the protection of granaries offices or warehouses, and for a number of
separate articles such as plate-chests or safes, a network of the threads or cords
may be employed, any one of which is capable of actuating the apparatus in the
same manner as the single cord or thread.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, 1 declare that what I
claim is :-
1. An apparatus for closing an electric circuit on the breakage or movement of
a thread or cord, constructed arranged and operating substantially as and for the
purpose herein before described with reference to the accompanying drawings.
2. In an apparatus for giving an electric alarm on the unauthorised opening of
a door window or other act, contacts normally held apart by an insulating ball
supported by a cord or thread arranged to be broken or moved by the unauthorised
act, such breakage or movement of the thread or cord operating to remove or
release the ball and to close the contacts, substantially as hereinbefore described
and as illustrated by the accompanying drawings.
Dated this 24th day of February A.D. 1892.
WILLIAM E. HEYS,
Agent for the Applicant.