When we need to monitor areas such as the living room, kitchen, bedroom, nursery or even the warehouse or office, we can use internal detectors. They have distinctly different characteristics from external ones, operate in a “more secure” environment and therefore have a more favorable situation.
The internal sensor is mounted more frequently on the wall to cover as wide an area as possible. Usually, the detection rate is 130-140 degrees at a distance of 8-20 meters or more. Pir-passive infrared (passive infrared detectors) are most used in anti-theft systems because they are cheap and very reliable, but we have to be careful.
As we have already seen, Pir sensors can read the energy radiated by the human body at a distance as it travels in front of them, and at that point, they send an alarm. Therefore, they are sensitive to sudden changes or sudden changes in temperature.
Thus, the internal infrared sensor does not need to be installed in rooms with equipment that causes rapid temperature changes. Therefore, they must be far from air conditioners, fans, boilers, but also smoke pipes. Attention should also be paid to reflective surfaces that move, mirrors that send the indicator “tilt”. Also away from direct light from spotlights or dots.
Also, be careful to install near a window, which, if it points to the road, can be distracting past car headlights, police sirens, and ambulances.
They are connected to the control unit via a wired system or a wireless system, in this latter case the power supply is taken from the batteries inserted into the sensor itself, which must be checked to prevent false alarm caused by the discharged battery.
If the conditions of the house or the environment in which they are installed are particularly difficult due to the abovementioned disturbances, the alternative is represented by microwave sensors.
How a microwave detector works:
double operation. The first uses a Gunn diode, which fills the room with electromagnetic waves with a certain amount of energy. This “stasis” status is saved. When the foreign body appears in the room, the energy used to saturate it is different, this variation triggers an alarm.
The second operation is related to the Doppler phenomenon, which is a physical phenomenon that is also utilized by radars. The sensor emits electromagnetic waves that hit an object that reflects part of the signal. If an object is stopped, the signal returned to the sensor will have the same frequency as the road, if it is different, or if something moves, the signal will start.
Also, in this case, the sensor may be subject to false alarms due to electromagnetic interference from other radio equipment in the house or due to the movement that the detector itself cannot interpret. For this reason, it is possible to install dual technology sensors that use both infrared and microwaves and only send an alarm after a double-check has given a positive result.