Door knob alarm device
AssigneeInternational Quartz Ltd.
InventorsHau C. Lam, Thomas K. P. Lee, Y. C. Cheng
Life of this patent
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Abstract
The 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.
Claims19
A doorknob alarm device comprising a body, means for hanging said device from a doorknob, electronic circuit means within said body including an oscillator circuit, a capacitance network coupled to the output of said oscillator circuit, an amplifier circuit coupled to the output of said capacitance network, means for electrically coupling said capacitance network to the doorknob so as to form an input to said electronic circuit means, self-initializing and self-compensating, oscillatory signal level detecting circuit means without manual sensitivity adjustment coupled to the output of said amplifier for detecting drops in the signal level from said amplifier such as would be caused by the addition of capacitance to said capacitance network when someone's hand comes close to or touches the doorknob on which said device is hung, an alarm circuit coupled to the output of said signal level detecting circuit, said alarm circuit being triggered by said signal level detecting circuit and a regulated D.C. power supply for supplying voltage to said electronic circuit means.
A doorknob alarm device comprising a body designed to be mounted on or near a doorknob, electronic circuit means within said body including, an oscillatory signal source having a self initiating and self-compensating output at which an oscillatory signal appears, an oscillatory signal detection circuit having a low gain for slow signal level fluctuations and a high gain for rapid signal level fluctuations and having no manual sensitivity adjustment, said detection circuit having an input and an output, a circuit network interconnecting said oscillatory signal source output and said detection circuit input and having a conductive path extending therefrom that can be placed in conductive contact with a doorknob on or near to which said body is mounted, and alarm generating means having a signal input connected to the output of said detection circuit for generating an alarm in response to a substantial change in the magnitude of the output of said detection circuit.
A doorknob alarm device comprising a body having an electronic circuit therein including an oscillatory signal source, an oscillatory signal change detection circuit, a circuit network interconnecting said oscillatory signal source and said detection circuit, a conductive path from said circuit network to a doorknob, alarm generating means coupled to an output of said signal change detection circuit for generating an alarm in response to a substantial change in the mangitude of the output of said detection circuit, and a coiled metallic spring connected at each end to said body and forming a loop adapted to be received over a doorknob, said spring being electrically coupled to said circuit network to form said conductive path and resiliently clamping said body to the shank of the doorknob thereby, not only to provide good electrical coupling between the doorknob and said circuit network, but also to mechanically hold said device in place on the doorknob.
In a doorknob alarm device of the type wherein a change in signal level in an electronic circuit within the device is generated as a result of a person coming near to or touching a doorknob to which the device is electrically coupled, the change in signal level being utilized to generate an alarm, the improvement comprising self-initializing and self-compensating signal level detecting means which do not have any manual sensitivity adjustment and which have low gain for a slowly changing signal level and a high gain for a rapidly changing signal level.
Dependencies are inferred from the claim text.