Intrusion detection with motion sensing

1. An intrusion detection system comprising:

at least two detectors, wherein each detector is configured to produce a detection output;

processors;

a memory storing instructions that, when executed by at least one processor among the processors, cause the intrusion detection system to perform operations comprising, at least:

producing metadata including information relating to adverse conditions that reduce detection performance of one or more of the at least two detectors; and

generating a combined alarm signal, wherein the combined alarm signal is a function of a plurality of detection outputs from the at least two detectors and the metadata.

2. The intrusion detection system according to claim 1 , wherein the function, for generating the combined alarm signal, is chosen to favor an output from one or more detectors whose performance is least affected by an adverse condition.

3. The intrusion detection system according to claim 2 , wherein the function is a weighted sum of detection outputs from the at least two detectors and the weighted sum depends on weighting factors corresponding to each of the at least two detectors.

4. The intrusion detection system according to claim 3 , wherein the weighting factors depend on the metadata.

5. The intrusion detection system according to claim 3 , wherein the metadata is received by the at least two detectors which apply the weighting factors to the detection outputs to produce weighted detection outputs; and

wherein the operations further comprise receiving the weighted detection outputs and determining the combined alarm signal.

6. The intrusion detection system according claim 1 , wherein the function is embodied as a table of combined alarm signal values indexed by at least one vector corresponding to the plurality of detection outputs from the at least two detectors and comprising values from a first plurality of possible values of the plurality of detection outputs and at least one value corresponding to the metadata.

7. The intrusion detection system according to claim 6 , wherein a smaller vector is computed having at least one combined value corresponding to a combination of one or more of the plurality of detection outputs and/or at least one value corresponding to the metadata to index a smaller table of alarm signal values.

8. The intrusion detection system according to claim 1 , wherein at least one of the detectors is a video motion detector (VMD) and at least one of the detectors is a passive infra-red (PIR) detector.

9. An intrusion detection system including:

at least two detectors wherein each detector is configured to produce detection outputs, one detector is a passive infra-red (PIR) detector, wherein the PIR detector includes at least two PIR sensors;

wherein the system is configured such that:

in non-adverse conditions each of the at least two PIR sensors must detect a target in order for the PIR detector to output a PIR alarm signal; and

in adverse conditions that affect PIR detection performance, the PIR alarm signal is output, if any one of the at least two PIR sensors detects the target.

10. The intrusion detection system according to claim 9 , wherein at least one of the detectors is a video motion detector (VMD) that has a field of view that at least partially overlaps the fields of view of the at least two PIR sensors.

11. The intrusion detection system according to claim 10 , wherein the VMD is configured to output metadata relating to the adverse conditions when the adverse conditions that affect PIR detection performance are detected.

12. The intrusion detection system according to claim 11 , wherein the metadata output from the VMD is received and processed by an analyzer.

13. The intrusion detection system according to claim 12 wherein the analyzer is further configured to send a control signal to the PIR detector when the adverse conditions that affect the PIR detection performance are detected by the VMD.

14. The intrusion detection system according to claim 13 , wherein the PIR detector is configured to receive the control signal and, when the control signal is received from the analyzer, output the PIR alarm signal if any one of the at least two PIR sensors detects the target.

15. The intrusion detection system according to claim 10 , wherein the VMD is configured to detect whether there has been a VMD tampering event, and if the VMD tampering event occurs, the VMD is configured to output metadata that includes an indication of the tampering event.

16. The intrusion detection system according to claim 15 , wherein when an analyzer receives metadata indicating VMD tampering the analyzer sends the control signal to the PIR detector to configure the PIR detector to require each of the at least two PIR sensors to detect the target in order for the PIR detector to output the PIR alarm signal.

17. The intrusion detection system according to claim 9 , wherein the at least two PIR sensors form corresponding pairs, wherein

at least one PIR sensor from each pair includes at least one emitter producing emissions that can be detected by the other PIR sensor or another suitable receiver.

18. The intrusion detection system according to claim 17 , wherein the system is configured such that a reduced intensity or non-detection of emissions by the other PIR sensor or the another suitable receiver is taken to be an adverse condition.

19. An intrusion detection system, the system including at least one video motion detector (VMD) and at least one passive infrared (PIR) detector, each detector being configured to output a detection output to an analyzer when the respective detector detects an intrusion event; wherein

the at least one PIR detector is used to determine a parameter of an intruding target; and

the at least one VMD independently determines a parameter of at least one target in a field of view of the VMD;

wherein if the parameter determined by the at least one PIR detector substantially matches the parameter of the at least one target independently determined by the VMD, then the analyzer is configured to send a control signal to the VMD and/or PIR detector such that the VMD and/or PIR detector sensitivity is increased when the control signal from the analyzer is received.

20. The intrusion detection system according to claim 17 , wherein if the parameter determined by the at least one PIR sensor substantially matches the parameter of the at least one target independently determined by the VMD, then the analyzer is configured to produce an alarm signal.

21. The intrusion detection system according to claim 17 , wherein the parameter determined by the at least PIR sensor and the parameter independently determined by VMD include any one or more of the parameters selected from the group of position, speed, size or direction.

22. The intrusion detection system according to claim 17 , wherein the analyzer is configured to send the control signal to the PIR detector to increase PIR detection sensitivity when a strong VMD signal is received by the analyzer; and

if the intrusion event is detected by the PIR detector, then the analyzer produces an alarm signal.

23. The intrusion detection system according to claim 17 , wherein the analyzer module is configured to send the control signal to the VMD to increase VMD detection sensitivity when a strong PIR detection signal is received by the analyzer; and

if the intrusion event is detected by the VMD, then the analyzer produces an alarm signal.

24. The intrusion detection system according to claim 23 , wherein the VMD detection sensitivity is only increased in locations corresponding to locations where the strong PIR detection signal is received.

25. The intrusion detection system according to claim 23 , wherein:

the strong PIR detection signal is an uncompensated signal so that alarm conditions can be determined remotely from the sensor; and

an ambient temperature is determined independently of the PIR signal and used in conjunction with the uncompensated PIR signal to determine the alarm conditions.