Door knob alarm device
Patent 4287513 Issued on September 1, 1981. Estimated Expiration Date: 
May 3, 1999. 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.
May 3, 1999. 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 3200306 3697971 Touch-responsive portable intrusion alarm Self-optimizing touch pad sensor circuit Pre-intrusion detection device Battery-operated body capacitance intrusion alarm apparatus Electronic security device Patent #: 4176348 InventorsAssigneeApplicationNo. 06/035721 filed on 05/03/1979US Classes:340/562, Capacitance307/125ElectricalExaminersPrimary: Swann, III, Glen R.Attorney, Agent or FirmInternational ClassesG08B 13/26 (20060101)G08B 13/22 (20060101) G08B 13/02 (20060101) G08B 13/06 (20060101) AbstractThe alarm device includes a resilient metallic spring strap which is received over a doorknob and against the shank of the doorknob and which forms an input contact to the device. The device further includes an oscillator which outputs a signal through a coupling network having a capacitive branch to ground that includes a capacitive path extending through the strap to the doorknob. When a person touches the doorknob, a capacitive path to ground is established that causes increased attenuation of the signal level. A self-initializing and self-compensating amplifier in the device detects such drops in the signal level and triggers a pulsating alarm. The circuit needs no manual adjustment.Field of SearchCapacitance | |
