Intrusion alarm system
First Claim
1. An obstruction resistant alarm system for detecting the presence of an intruder in a location being monitored, comprising:
- a housing including a selectively transmissive window that transmits radiation within a first wavelength range and scatters radiation within a second wavelength range;
an intrusion sensor positioned to receive from an intruder radiation of wavelengths within the first wavelength range passing through the window, the intrusion sensor producing in response to the radiation within the first wavelength range a presence signal indicative of the presence of the intruder in proximal location to the intrusion sensor;
a radiation source emitting and a radiation detector detecting radiation within the second wavelength range, the radiation source positioned to direct the radiation within the second wavelength range to strike and then be scattered by the window and the radiation detector positioned to detect the radiation within the second wavelength range striking and scattered by the window, such that the radiation within the second wavelength range emitted by the radiation source and scattered by the window forms a normal radiation pattern having a normal intensity detected by the radiation detector whenever the window is unobstructed and an abnormal radiation pattern having an abnormal intensity detected by the radiation detector whenever the window is obstructed; and
an alarm circuit operatively connected to the radiation detector to produce an alarm signal in response to detection by the radiation detector of radiation intensity corresponding to an abnormal radiation pattern to indicate an obstruction of the window and a consequent compromise to the reliability of the presence signal produced by the intrusion sensor.
5 Assignments
0 Petitions
Accused Products
Abstract
An obstruction resistant alarm system for detecting the presence of an intruder includes a housing (2) having a selectively transmissive window (1) that transmits radiation within a first wavelength range and scatters radiation within a second wavelength range. An intrusion sensor positioned to receive from an intruder radiation of wavelengths within the first wavelength range that pass through the window produces a presence signal that indicates the presence of the intruder. A radiation source (20) is positioned to direct radiation within the second wavelength range to strike and then be scattered by the window. A radiation detector (21) is positioned to detect the radiation striking and scattered by the window. The radiation emitted by the radiation source and scattered by the window forms a normal radiation pattern having a normal intensity whenever the window is unobstructed and forms an abnormal radiation pattern with an abnormal intensity whenever the window is obstructed. An alarm circuit (19) produces an alarm signal whenever the radiation detector detects radiation intensity corresponding to an abnormal radiation pattern to indicate an obstruction of the window and a consequent compromise to the reliability of the presence signal produced by the intrusion sensor.
61 Citations
10 Claims
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1. An obstruction resistant alarm system for detecting the presence of an intruder in a location being monitored, comprising:
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a housing including a selectively transmissive window that transmits radiation within a first wavelength range and scatters radiation within a second wavelength range; an intrusion sensor positioned to receive from an intruder radiation of wavelengths within the first wavelength range passing through the window, the intrusion sensor producing in response to the radiation within the first wavelength range a presence signal indicative of the presence of the intruder in proximal location to the intrusion sensor; a radiation source emitting and a radiation detector detecting radiation within the second wavelength range, the radiation source positioned to direct the radiation within the second wavelength range to strike and then be scattered by the window and the radiation detector positioned to detect the radiation within the second wavelength range striking and scattered by the window, such that the radiation within the second wavelength range emitted by the radiation source and scattered by the window forms a normal radiation pattern having a normal intensity detected by the radiation detector whenever the window is unobstructed and an abnormal radiation pattern having an abnormal intensity detected by the radiation detector whenever the window is obstructed; and an alarm circuit operatively connected to the radiation detector to produce an alarm signal in response to detection by the radiation detector of radiation intensity corresponding to an abnormal radiation pattern to indicate an obstruction of the window and a consequent compromise to the reliability of the presence signal produced by the intrusion sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification