Method and apparatus for prefiltering received messages in a security system

1. In a security system comprising a plurality of wireless transmitters, each having a unique identification number, at least one wireless receiver module in communication with each of the transmitters, and a control panel connected to the receiver module for processing signals sent from the transmitters to the receiver module, a method of prefiltering the received wireless signals comprising the steps of:

a) generating a prefiltering map comprising the steps of:

i. for each of the transmitters in the security system, performing an algorithm on the identification number of the transmitter;

ii. storing the result of the algorithm in a prefiltering map;

b) storing the prefiltering map in the receiver module;

c) for each wireless message received by the receiver module from a transmitter, the receiver module performing the steps of:

i. extracting from the message the identification number of the transmitter that transmitted the message;

ii. performing the algorithm on the extracted identification number;

iii. comparing the result against the prefiltering map in the receiver module;

iv. forwarding the message to the control panel if the comparison result is true; and

v. discarding the message if the comparison result is false;

wherein the prefiltering map is not modified as a result of forwarding the message to the control panel if the comparison result is true or discarding the message if the comparison result is false.

2. The method of claim 1 in which the step of performing an algorithm on the identification number of the transmitter comprises the step of performing a hashing function on the identification number.

3. The method of claim 2 in which the step of performing a hashing function produces an N-bit result, wherein N is in the range of 4-8 bits.

4. The method of claim 3 in which the prefiltering map has 2 N bit positions, and in which a bit is set in the map in the position that corresponds to the result of the hashing function for each transmitter.

5. The method of claim 4 in which the comparison result is true when the result of the hashing function for a received transmitter message has a bit set in the prefiltering map.

6. A security system comprising:

a) a plurality of wireless transmitters, each comprising a unique identification number,

b) at least one wireless receiver module in communication with each of the transmitters, and

c) a control panel connected to the receiver module for processing signals sent from the transmitters to the receiver module, wherein the control panel comprises:

i. means for generating a prefiltering map for storage at the receiver module, said means comprising means for performing, for each of the transmitters in the security system, an algorithm on the identification number of the transmitter; and

ii. means for assembling the results of the algorithm into a prefiltering map; and

wherein the at least one wireless receiver module comprises

i. means for storing the prefiltering map obtained from the control panel;

ii. means for extracting, from each wireless message received by the receiver module from a transmitter, the identification number of the transmitter that transmitted the message;

iii. means for performing the algorithm on the extracted identification number;

iv. means for comparing the algorithm result against the prefiltering map in the receiver module;

v. means for forwarding the message to the control panel if the comparison result is true; and

vi. means for discarding the message if the comparison result is false;

wherein the prefiltering map is not modified as a result of forwarding the message to the control panel if the comparison result is true or discarding the message if the comparison result is false.

7. The system of claim 6 in which the means for of performing an algorithm on the extracted identification number of the transmitter comprises means for performing a hashing function on the identification number.

8. The system of claim 7 in which the means for performing a hashing function produces an N-bit result, wherein N is in the range of 4-8 bits.

9. The system of claim 8 in which the prefiltering map has 2 N bit positions, and in which a bit is set in the map in the position that corresponds to the result of the hashing function for each transmitter.

10. The system of claim 9 in which the comparison result is true when the result of the hashing function for a received transmitter message has a bit set in the prefiltering map.

11. A wireless receiver module for use in a security system comprising:

a) means for storing a prefiltering map, the prefiltering map comprising a plurality of bits, each of the bits corresponding to the result of an algorithm performed on a transmitter identification number;

b) means for extracting, from a wireless message received by the receiver module, an identification number of a transmitter that transmitted the message;

c) means for performing the algorithm on the extracted identification number;

d) means for comparing the algorithm result against the prefiltering map;

e) means for forwarding the message to a control panel wired thereto if the comparison result is true; and

f) means for discarding the message if the comparison result is false;

wherein the prefiltering map is not modified as a result of forwarding the message to the control panel if the comparison result is true or discarding the message if the comparison result is false.

12. The receiver module of claim 11 in which the algorithm is a hashing function.

13. The receiver module of claim 12 in which the hashing function produces an N-bit result, wherein N is in the range of 4-8 bits.

14. The receiver module of claim 13 in which the prefiltering map has 2 N bit positions, and in which a bit is set in the map in the position that corresponds to the result of the hashing function for each transmitter.

15. The receiver module of claim 14 in which the comparison result is true when the result of the hashing function for a received transmitter message has a bit set in the prefiltering map.

16. A control panel for use in a security system comprising:

a) means for generating a prefiltering map, said means comprising means for performing, for each of a plurality of transmitters enrolled in the security system, an algorithm on the identification number of the transmitter;

b) means for assembling the results of the algorithm into a prefiltering map; and

i. means for transferring the prefiltering map to a wireless receiver module connected thereto.

17. The control panel of claim 16 in which the means for performing an algorithm on the identification number of the transmitter comprises means for performing a hashing function on the identification number.

18. The control panel of claim 17 in which the means for performing a hashing function produces an N-bit result, wherein N is in the range of 4-8 bits.

19. The control panel of claim 18 in which the prefiltering map has 2 N bit positions, and in which a bit is set in the map in the position that corresponds to the result of the hashing function for each transmitter.