Improvements in Burglar Alarms.
Year: 1887

page_text: COMPLETE SPECIFICATION.
Improvements in Burglar Alarms.
I, JAMES DOUGLAS DALLAS, of 254 West 24th Street, in the City, county, and
State of New York, in the United States of America, Electrician, 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
--
In a burglar alarm constructed according to my invention, a solenoid in an
auxiliary electric circuit connected to a small battery and closed when the window or
door is shut attracts an armature; but when the window or door is open the said
armature is drawn by a spring against a stop and closes a main electric circuit
connected to the main battery and containing an indicator and a bell, and thus causes
the bell to ring.
When applying my apparatus to more than one window or door, the terminals of
each auxiliary circuit may be connected to the terminals of the same small battery;
and the small bell and main battery may be employed for each main circuit, the
indicators shewing which auxiliary circuit has been broken.
The accompanying diagram shows my improved alarm as applied to two windows
or doors.
Two strips of copper A are fixed to each door or window to be protected and a
spring B of steel or other suitable conducting material is so arranged with respect to
the strips A that when the window or door is closed, it makes contact with both.
A copper wire connected to one pole of a small battery C is connected to one strip A
on each window or door; and the other strip A of each window or door is connected
to one terminal of a separate solenoid D; the other terminals of the solenoids are
connected to the other pole of the battery C.
Each solenoid D is provided with a separate armature E; springs F tend to draw
the armatures away from the solenoids against the contacts or stops G, each contact
or stop G is connected to one terminal of a separate indicator H; the other terminals
of the indicators H are connected to one terminal of an electric bell L whose other
terminal is connected to one pole of a main battery M; the armatures E are all
connected to the other pole of the battery M.
It will readily be seen that when the windows and doors are closed the circuits
гр.

page_text: containing the solenoids D are closed and the solenoids attract their armatures away
from the stops G; but when any window or door is opened, the current passing
through that solenoid D corresponding to the open window or door is stopped; and
that armature E of that solenoid is then drawn against its contact G and completes
the circuit from the main battery M through the indicator H corresponding to that
solenoid and through the bell L. The bell is thus caused to sound the alarm and the
indicator shows which particular window or door has been opened.
Any suitable form of indicator may be used, such as those usually employed in
hotels to indicate from which room a bell has been rung. Separate batteries may be
employed if desired for each window or door.
One advantage of my apparatus is that if the contacts A. B. get out of order, the
bell will ring and the indicator will show the particular contact.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
1. In a burglar alarm, arranging the main electric-circuit containing the bell to be
kept open by means of a solenoid in an auxiliary circuit closed when the window or
door is open, the said solenoid then attracting a spring armature which breaks the
main circuit.
2. A burglar alarm consisting of a main circuit containing a battery and bell and
as many spring contacts and indicators as there are windows and doors to be
protected; and of as many auxiliary circuits as there are windows and doors to be
protected; each auxiliary circuit containing a separate solenoid and being completed
by contacts of a corresponding window or door when closed, and each solenoid when
its circuit is closed attracting the spring contact so as to open the part of the main
circuit containing the corresponding indicator so that when all the windows and doors
are closed, the main circuit will be completely broken and so that a corresponding.
part of the main circuit will be closed when any window or door is opened and
operate the corresponding indicator and the bell.
3. The. arrangement of a burglar alarm substantially as described and illustrated.
Dated this 8th day of December 1887
WHEATLEY & MACKENZIE,
156, Strand, W.C., Agents.