They are not reliable and are dead on warning when a transmitter operates in a condition who muzzle the wireless alarm system.
This is easily done with Radio Transmitters operating:
- ON the wireless frequency
- Saturating the receiver
- Intermodulation
- Harmonics
- Falling in the receiver bandpass
- On the IF frequency
- and more... This is what i call basically Radio Frequency Interferences (RFI) but in fact it covers, like you can notice above a lot more.
In essence the problems is the fact that by no way two (or more) systems can use simultaneously the same frequency, its called collisions, interferences and more like you see above.
The WORST is that the OWNER DON'T KNOW THAT HISS alarm system is no longer operational, no message (20 years records hold by so called experienced professionals: no RFI alarm).
Use a wired systems and use WIRELESS only when impossible to wire, but BE AWARE that YOUR SAFETY IS HAZARDOUS (my system was dead during more than one year before i found out by accident and measuring the wireless receiver output signal content). Muzzling can occurs permanently or occasionally, mine was permanent.
Note: So called low level mechanically (who claim them self professional) try to let you believe that my system was dumb and/or badly installed and they don't realize that it is an external influences that can't be avoided whatever wireless alarm system you have. Its a pure radio communication problem know by telecommunication specialists. There is a way around for $$$ investments but that is out of reach of a wireless alarm system.
Paul NOTE: My system is replaced with a wired one, do the same.