44. Why are wireless alarm systems...

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Why are wireless alarm systems sensitive to Radio Frequency
Interferences (RFI)?

House alarm wireless systems with theyre 10 milliWatt sensor
transmitter power are ONLY allowed to operate on 434 MHz and/or 868
MHz.
 Those frequencies are provided for free general use, they are
uncontrolled, unprotected against disturbances.
 Those frequencies are very crowded with all kind of non alarm purpose
equipment.
 More, the very low power (<10 milliWatt) of the transmitters
contained in the sensors make the receiver very sensible to external
unwanted signals called RFI..

Even in a normal undisturbed frequency condition the reviver signals
from the sensors are week and require attention subject location.
 Its why "some" wireless alarm systems are equipped with a signal
monitoring circuit to help correct installation.