Alarm system including remote signalling means

#The present invention generally relates to alarm systems, and more specifically to an alarm system which includes one or more remote stations connected to a control station by only three leads but which nevertheless permits remote control of the alarm system and which provides numerous visual indications of the status of the alarm system at the central as well as remote locations.

#There are numerous alarm systems, including intrusion as well as fire, already known. While the basic circuitry of such alarms is relatively simple, many of the known alarms incorporate means for increasing the effectiveness of the alarm system, decreasing the number of false alarms, minimizing power consumption or preventing tampering with the system. Typical alarms of the aforementioned types are disclosed in U.S. Pat. Nos. 3,351,934; 3,641,552 and 3,828,340.

#The use of remote stations which permit supervision of the alarm system are also known. With such an arrangement, there is typically provided central control box which includes the bulk of the circuitry of the system as well as the power supplies and stand-by batteries for energizing the system. The control boxes are normally concealed and locked so that tampering therewith is not possible without actuating the alarm. When remote stations are provided, these are connected to the control box and permit limited control of the alarm system. Sometimes, the remote stations provide an indication of the status of the alarm system. U.S. patents which disclose alarm systems having remote stations are U.S. Pat. Nos. 3,174,143 and 3,747,093. The use of LEDs in alarm systems is also known and disclosed in U.S. Pat. No. 3,706,987.

#FIG. 1 is a schematic representation of an alarm system in accordance with the present invention, showing a remote station having an indicator light and a key switch connected to a central or control station by only three leads;

#FIG. 2 is a schematic representation, partially in block diagram form, showing the details of the control station and remote station shown in FIG. 1, and further showing the manner in which a plurality of remote stations are connected parallel to each other and connected to the control station by only three leads or conductors;

#FIG. 3 is similar to FIG. 2, but only showing the details of the alarm system at the control station during a non-alarm condition of the system, as opposed to the alarm condition shown in FIG. 2; and

#Referring to the figures, wherein the similar or identical parts are identified by the same numerals throughout, and first referring to FIG. 1, an alarm system in accordance with the present invention is generally designated by the reference numeral 10.

#The alarm system 10 includes a control station 12, the circuitry of which is generally housed within a control box 14 which is made tamper proof and concealed.

#Most simple present-day alarm systems include a single closed "instant loop" and are known as "closed loop" systems. Such a closed instant loop is designated by the reference numeral 16 in FIG. 1, and such a loop is generally preferred because it is somewhat more effective and tamper proof than "open loop" systems. While the "closed loop" alarm systems require a continuous flow of current through the loop during the non-alarm condition, these currents can be made sufficiently small so that there is minimal drain on the source of electrical energy. Such simple, closed instant loops used for intrusion alarm systems typically include switches at the openings to the premises to be protected, including doors and windows, which switches are closed during the non-alarm condition when the openings are also closed. When one of the openings is violated, the respective switch associated with that opening breaks or opens the loop to interrupt the current flow therethrough. Such termination of current flow is detected by the alarm system and suitable visual or audio indications may be provided. The opened loop is designated by the reference numeral 16' in FIG. 2.