To detect a presence, wireless motion detectors generally use harmlessinfra-redtechnology. However, on detection of a presence they are normally the only sensors to communicate with the central alarm on a regular basis using radio frequencies on average every one to three minutes. This means that you can be exposed all day in your home so it is advisable to avoid using wireless detectors.
In order to use wireless detectors without risk of exposure, a solution has been found by the company RISCO
Reminder concerning wireless alarm systems
Domestic wireless alarm systems generally use standard frequencies of 434 MHz & 868 MHz for communication between the various elements (sensors, detectors, keyboard, siren etc.) and the central alarm.
In order to use wireless presence sensors
without initiating regular exposure to waves, a solution has been found by RISCO. To my knowledge, only Risco alarms (at the time of writing this report) have solved the problem of being subjected to the effects of regular communication between the wireless sensors and the central alarm when you are at home.
Communication between the sensors and the central alarm system
Communication frequency can vary between 1 & 3 minutes according to the timing programmed for the sensor. The sensor detects your presence, communicates with the central alarm then activates a timing of 1 to 3 minutes during which period there are no emissions. This avoids the batteries discharging too quickly.
After this timing, the sensors communicate once again with the central alarm if your presence is still detected in the room. These sensors are unidirectional.
The RISCO solution : bi-directional sensors
When the alarm is not activated, the “bi-directional” sensor only communicates when interrogated by the central alarm system.
This is programmed when the technician installs the alarm system. Parameters : Rx = 0 ; TX = 0; signifies that there is no established communication between the sensors and the alarm so long as the alarm is not triggered.
The alarm is activated only when you leave home.
Material used for the test
Calibrated spectrum analyser NARDA SRM 3006: effective radiation measure and visualisation of emission frequency.
To record alarm radiation levels:
HF59B + antenna UBB27 + Filter FF6 (position LP <1000) + NFA 1000 (recording support).
Recording of wireless communications in test mode
In this mode the central alarm regularly interrogates its sensors to check communication quality. This mode is used when the alarm is installed.
Electromagnetic radiation measures: (in the case of a sensor communicating regularly)
Emission frequency of radiation from sensors
Two frequencies are used for communication between the sensors and the central alarm: 868.63 MHz & 869.53 MHz
At one meter from the sensor: 353 mV/m : significant radiation
Up against the sensor: 1.5 V/m : very strong radiation
RISCO bi-directional sensors
So long as the alarm is not activated and even if you are present in the home, it never communicates with the central alarm via radio waves. This allows the installation of wireless presence sensors while remaining protected on a daily basis from electromagnetic radiation.
The mode without bi-directional sensors
(configuration RX = 0 ; TX = 0 ; at the level of the central alarm) :
In this mode a recording has been carried out every 24 minutesand shows a total absence of communication between the central alarm and its sensors.
Recording of the amount of radiation emitted over 24 minutes
In this mode a recording has been carried out every 24 minutes and shows a total absence of communication between the central alarm and its sensors.