Patent ID: 7724134

Claim:
A method for detecting at least one of a fire and an intruder using passive reception of microwave radiation, comprising: passively receiving a first microwave radiation signal at a first receiver, said first receiver including a first antenna, a first frequency of said first passively received microwave radiation signal being indicative of a temperature of a source of said first passively received microwave radiation signal; passively receiving a second microwave radiation signal at a second receiver, said second receiver including a second antenna, a second frequency of said second passively received microwave radiation signal being indicative of a temperature of a source of said second passively received microwave radiation signal, wherein said first and second frequencies are within a range of microwave frequencies protected from active transmission in a geographic area encompassing a location of said first and second receivers; comparing said first frequency with said second frequency to determine a presence of at least one of a fire and an intruder; and transmitting said first and second passively received microwave radiation signals to a signal processor; said first passively received microwave radiation signal being converted to a first voltage signal; said second passively received microwave radiation signal being converted to a second voltage signal; said first voltage signal being subtracted from said second voltage signal to provide a resulting voltage signal; and said presence of said at least one of said fire and said intruder being determined based on said resulting voltage signal.