Motion sensor: how it works

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Alejandra Rangel

How a motion sensor works

If you agree, I'd start by talking to you about how a motion sensor works. Well, a motion sensor - also called motion detector - is based on a infrared radiation. You must know that the infrared radiation of light constantly passes through all bodies (animate and inanimate objects of any kind) and releases energy that transforms into heat. The motion sensors are able to detect the infrared radiation radiated, in return, by the bodies that are in their range of action.

For this reason, devices of this kind are also called PIR sensor (where PIR stands for Passive InfraRed, ie "passive infrared"). The technology of infrared motion sensors is in fact passive, since these sensors are designed to passively “capture” the radiation and energy (heat) radiated by other bodies. Sensors of this type, therefore, are able to detect temperature variations in the range of action (the latter is generally equal to about 10 meters, with the more "performing" models reaching up to about 30 meters with various angulation radii, in general 180 ° o 360 °).

It is therefore logical that sensors of this kind should be placed far from devices capable of modifying the temperature or emitting heat (air conditioners, ovens, radiators and the like). Furthermore, the sensors should also be placed away from mirrors or other reflective surfaces that could “bounce” the infrared radiation causing false detections.

Some motion sensors (generally more expensive), in addition to infrared, also take advantage of Microwave and through these it is possible to detect the movement of a body. In this case the sensor emits a radiation and detects the return radiation: if the latter has the same frequency, the detected body is stationary; if, on the other hand, the frequency is different, the body is perceived as moving (effect Doppler ).

Other sensors equipped with microwave technology are able to saturate the surrounding environment with a certain amount of energy and, as soon as a variation in this "equilibrium" state is detected, the sensor is forced to introduce more energy into the environment to restore the balance and, as the consumption of the device increases, the intrusion is detected.

Finally, some sensors (as well as exploiting infrared radiation and microwaves) also have technology DMT, that is, they are able to perform short-range and large-range detections. By alternating these "scans" they make them very accurate (in this way "false alarms" are avoided). The ones I have listed so far are the most popular detection technologies, but there is no shortage of models that also integrate detection a ultrasound and that of vibrations.

Motion sensors are typically used in the safety (they are placed in strategic points, of mandatory passage, inside or outside buildings to monitor the environments) andautomation (for example, they can be plugged into an electrical outlet to automatically turn on the devices connected to the outlet).

The anti-intrusion motion sensors used in the security sector (in the anti-theft systems) are generally connected to an external control unit which is able to record and analyze the signals sent by them via radio waves or via wires. In case of intrusion detection, the control unit activates the acoustic signal of the alarm siren (the most modern control units can also contact all the users registered in their virtual address book by telephone or with automatic SMS).

Several sensors can be connected to the same control unit at the same time, depending on the extension of the environment to be monitored and the sensors are generally able to send a signal to the control unit even in the event of manumission o application of objects to act as a screen (in some cases these sensors are equipped with a siren and work without a control unit). Sensors fall into the category of motion sensors in alarm systems perimeter and those volumetric.

The former are applied (usually with double-sided tape or with various types of supports) in the gates of a building, i.e. the points of access to it (doors, windows, etc.). The sensors "the tent", generally of small dimensions, are mounted on the frame of doors and windows, are generally battery powered (the latter must be replaced periodically, within a few years) and detect intrusions from the outside (in this case, therefore, the window or the door they "oversee" can be left either closed or open).

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Other sensors (called "At the door"), very similar in appearance to the latter, are instead mounted directly on the internal part of doors or windows and not on the frames of the latter. In this case the sensor will detect any movement of the surface on which it is applied (for example, if a window is forced it vibrates and the sensor will detect the anomaly by sending the signal to the control unit). In general, in order not to spoil the aesthetics of doors and windows, curtain sensors are preferred that remain external to the building (moreover, the latter type of sensors, unlike the "door" ones, does not make it necessary to keep the closed windows).

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Motion sensors volumetric they are usually larger than those I have told you so far, they can be used inside the rooms (they can also be used on terraces and other outdoor spaces) and they are able to detect the presence of foreign bodies in the environment in which are positioned (they can detect both the heat be it air displacement). Some of these sensors are also able to distinguish between people, animals and objects (in the case of animals they avoid false alarms and are indicated with the words Pet immune).

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All the sensors I mentioned earlier can be deactivated if necessary and the price varies from about 10 € to various tens of euros (in some cases even more than 100 € sensor) based on the technology used (infrared, microwave and DMT), range of action, power supply and accuracy of detection (distinction between people, animals and objects). Furthermore, it is very likely to find all these sensors included in an anti-theft system “package” with control unit included (some of them “loose” are only compatible with some control units).

My advice, in any case, for the assembly of these devices, is to contact a specialized technician since most of the defects in their functioning are due to errors in the installation phase. Motion sensors that do not fall into the category of those in the security field are mainly used in the home environment (and in commercial premises) to regulate thelighting of the environments.

By connecting one of these sensors to an electrical outlet, for example, the sensor can automatically turn on the lamp it is connected to when it detects the presence of a person in its range. This way a lot of energy can be saved when lighting is not needed. Some of these sensors are also able to detect the change between day and night and “act” accordingly. I'll tell you more about these sensors later.

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Twilight motion sensor: how it works

Some lamps are equipped with twilight motion sensor. Sensors belonging to this category are able to perceive the type and intensity of light in the environment in which they are located. A sensor of this kind can be combined with a switch which is activated and deactivated according to the signal emitted by the sensor.

Generally speaking, when the light falls below a certain threshold of luxury (the unit of measurement relating tolighting), the sensor emits a signal that activates the switch it is connected to. The sensor can be equipped with various components capable of perceiving light and generating a flow of electrons as a response: fotoresistenze, photodiodes and / or phototransistor (based on these components the sensor is more or less reactive, the phototransistor has a much higher sensitivity than the photodiode but compared to this it is slower to emit the pulse).

Upon receiving the signal, the switch contacts (or does not) the electrical contacts of the circuit to which it is connected and in this way the lamp to which it can be connected turns on and off. The vast majority of these sensors are used in contexts "External". Lamps, street lamps and other lighting systems placed outside homes or on the streets are currently equipped with a sensor that falls into this type and makes it possible to use "intelligent" energy avoiding waste of any kind.

Furthermore, some of these sensors (the most recent ones) are also able to distinguish artificial light from natural light so as to avoid the hypothesis of malfunctions.

By special wiring the twilight motion sensors must be connected to the lighting device and as regards the power supply, it can be done by connecting to theelectrical system, the battery or with solar panel (Most wired sensors include very detailed artwork on how to connect using cables, so don't let this worry you too much.)

For many of these sensors there is also the possibility to manually adjust the degree of sensitivity to light and the time of activity starting from the detection of the change of lighting (by setting the maximum degree of sensitivity, the sensor is activated even when the light is not very intense, such as during the last hours of sunset).

Prices vary according to light sensitivity, to any other combined technologies (also in this case the sensors can also detect movement through infrared, Microwave e DMT), reaction times and degree of protection against bad weather (they are normally water resistant); it starts from a handful of euros up to a few tens (between 20 and 30 € for the more expensive models).

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Motion sensor lamp: how it works

I motion sensors they can be used in the most varied contexts, in addition to that of safety (which is perhaps the most commonly associated scope with this type of device). Suffice it to say, for example, that various types of lamps e bulbs equipped with motion sensors.

Are you wondering what a motion sensor in a lamp is for? Simple: to allow it to turn on and off. Basically, the sensor, using one of the technologies I told you about in the first chapter of the tutorial (detection a infrared, Microwave and / or DMT), detects movement or the presence of a body in a given range of action and turns the lamp switch on or off.

For example, if you install a lamp of this type near a sink, it will turn on every time you approach it to wash your hands and it will go out when you leave. Really comfortable, right? This is a particularly functional solution to avoid waste of energy and achieve a certain "visual impact".

In addition, sometimes, the sensors of these lamps are also set up to detect the movement of objects such as, for example, one port or a window, in order to illuminate an internal environment if necessary. Lamps of this kind are widely used especially in public and commercial establishments but are gradually spreading also in the home environment. Many of these lamps can be oriented in various ways and set the activation time starting from the detection of movement by the sensor.

The power supply can take place by connecting to theelectrical system, the battery or through any solar panels. As for the types and models (standard lamps, floor lamps, LED headlights, spotlights, street lamps and lanterns) they differ greatly depending on the use and the area of ​​destination and, first of all, if they are outdoor lamps. or indoors. The intensity of the light emitted is also variable and so are the colors (by combining various lamps of different colors together, rather “refined” effects can be obtained.

As far as prices are concerned, in this case it is difficult to indicate a range given that, due to their extremely multifaceted nature. It is generally necessary a few tens of euros depending on the intensity and type of light emitted, the range of action, the reactivity of the sensor and the design of the lamp itself.

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Motion sensor camera: how it works

also the cameras can be equipped with motion sensors. This type of device is generally used in the field of safety (to monitor shops, public places and homes). There are, however, other areas of use, such as the surveillance of pets or very young children.

Cameras of this type, integrating the same sensors I told you about at the beginning of the tutorial, detect movements within their visual range and can send a signal to the external control unit (if connected to a anti-theft system) or phone of the person who installed them, via notification (many of them, in fact, can be associated with uses for Android and iOS / iPadOS devices) e-mail o SMS (some of them are equipped with a card slot SIMs.).

The sensors of some of these cameras are also able to distinguish between the type of moving bodies and those that do not report the passage of animals are called Pet immune. Upon receipt of the notification, the applications associated with these cameras allow you to show the video stream coming from the camera on the device on which the app is installed in a handful of taps in order to immediately check for any false alarms.

It goes without saying, therefore, that this type of these cameras are equipped with a chip for the connection Wi-Fi or entry for connection Wired internet. Usually the sensor can be deactivated (via physical button or via app) and some of these cameras are also equipped with a speaker thanks to which your voice can be transmitted via the app (for example, if you are supervising a child, you can communicate with it in this way).

By inserting a memory media (such as a microSD card), you can shoot snapshots o to record, if necessary, the video stream of the camera, moreover, the most recent models are also able to store on the in cloud (i.e. on a server on the Network) recordings (this function may require the payment of an additional cost depending on the camera manufacturer).

This type of camera must therefore be installed within the range of the Internet network (if you use Wi-Fi, in case you can also use a signal repeater) and as regards the power supply, you can connect the camera to theelectrical system, The one solar panel or take advantage of the integrated battery (the latter generally lasts a few months even if the camera is always on).

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Prices vary from 45-50 euro to a few hundred euros, depending on the type of power supply (those equipped with solar panels are generally more expensive), shooting quality (the most common standard is the Full HD), zoom and coverage range, the ability to shoot even in the dark with night light, type of motion sensor, battery life and type of weather protection.

Motion sensor: how it works

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