Method and system for determining the presence of objects within a particular surveillance area, in particular for prevention of shoplifting
Patent 4123749 Issued on October 31, 1978. Estimated Expiration Date: 
March 28, 1997. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
March 28, 1997. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References 3765007 3820104 3838409 InventorsAssigneeApplicationNo. 05/782098 filed on 03/28/1977US Classes:340/572.1Detectable device on protected article (e.g., "tag")ExaminersPrimary: Swann, III, Glen R.Attorney, Agent or FirmInternational ClassG08B 13/24 (20060101)Foreign Application Priority Data1976-04-03 DEAbstractA surveillance system for preventing shoplifting comprises marking elements made of material of high magnetic permeability attached to the goods in a store, and magnetic field generating coils generating a magnetic field in the exit areas from the store. Two different alternating magnetic fields are produced on opposite sides so that the configuration of the field within the exit area is continuously changing. Introduction of a marking element into this area causes different frequencies to be produced which are sensed by a sensing element which then emits a signal. The marking elements can be deactivated during a normal purchase by magnetically saturating the material. | |
