The most important things to know

to choose meaningfully.


Intrusion sensors are devices created with the scope of detecting the access or attempted access, of someone into a specific protected area. When these sensors detect activity, they notify the central hub, which in turn activates other devices.

In the beginning, it is reasonable to associate intrusion sensors with door and window sensors. These devices detect when an entry point is being forced or opened and communicate with the hub that subsequently activates a siren. However, the application fields covered by intrusion sensors are much broader.

Within the security area, you can find different types of sensors according to the goal pursued. You can install motion sensors within your house to know when someone is approaching a sensible area, or you can, for instance, install buried pressure sensors outdoors to know when someone has entered your premises without authorisation. Additionally, thanks to the flexible positioning offered by the wireless sensors and the possibility to connect them to the internet, you can apply the same sensors used for your doors or windows as well in locations more out of reach and track each of them from remote. This possibility can be especially useful if you are sharing a flat, have kids, pets or in case you use home services like house-cleaning. What if you could be notified when the closet containing your favourite chocolate is opened? What if, while you are away, an indoor security camera could start registering when the cabinet is opened? What if you could use the two-way communication feature of the security camera to talk to the intruder, and use your negotiation skills to convince him about blowing over the initial idea?

In addition to security purposes, intrusion sensors are widely used to automate other aspects of your home. Either you want to turn on the lights of your living room and play some relaxing music by the time you open the main door of your home, or you want to turn off the heating by the time you open the windows in the morning. The number of scenes that can be created is countless.

Self-monitored security cameras, remote professional surveillance or physically present security guards are some additional alternatives that can be chosen or combined with to increase the security of your home. However, the right selection and combination of self-monitored intrusion sensors remain as the most cost-effective and easy to implement a solution to detect potential break-ins in your home.


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Time saved thanks to the possibility of monitoring the status of several areas of your home without displacements.

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No direct impact on the physical environment.

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Peace of mind increased thanks to increased visibility on any non-desired movement at home and a decreased reaction time in case of a break-in.

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No direct impact on home costs.


Intrusion sensors can be of different types. If we consider the type of installation, sensors can be surface-mounted and visible to the eyes or recessed and covered to difficult their detection. They can be powered by wires or batteries and used to monitor outdoor or indoor spaces. However, these are aspects that can be shared among the different types of intrusion sensors when they are classified attending their essential operating principles. Hereafter follows an overview of the most common operating principles used to classify intrusion sensors:

These are one of the most used intrusion sensors and can usually be found on doors and windows. They consist of a detecting magnet also known as a switch, generally attached on the fixed part of the opening, and a magnet, installed on the mobile part. These two components generate a magnetic field around them that is interrupted when the entry point is opened. In that situation, the detecting magnet detects the difference and alerts about the opening. Magnetic switches can be used on other applications like closets or to secure objects in a fix position. Additionally, it is worth knowing that some of these intrusion sensors come with balanced switches (Balanced Magnetic Switches) that create a secondary magnetic field to help to prevent defeat.

Generally installed on walls or ceilings, these sensors are used to detect when a glass is broken. When glass breaks, it emits soundwaves at a specific frequency that is recognised by the sensor, generating in this way an alert. The disadvantage of acoustic sensors relies on the possibility of experimenting false alarms when, for instance, you break a cup, shake some keys or operate some machinery.

These shock sensors detect the movement of the surface to which they are secured. They are generally attached on doors, glasses and walls, but it is essential to know that not all vibration sensors may be able to detect the movement on all types of surfaces. This is because each surface has its' own structure and consequently, they vibrate at different frequencies. One of the main advantages of vibration sensors is that they can detect break-in attempts before they happen. On the other side, although they are designed to ignore normal building vibrations, on some occasions, they can be the source of false alerts.

These sensors are generally used in entry points like garages, doors and gates. They consist of a transmitter that emits a beam of infrared light to a receiver. When the beam is interrupted by any object, an alert is generated. For security purposes, the beam can be made invisible, and if needed, a series of transmitters and receivers can be combined to increase the number of beams and with this extend the area covered.

The application of capacitance sensors is limited to metal objects like safes or file cabinets, and they work using the same principle of capacitors. The metallic objects to be protected present insulation feet that separate them from an electrical ground plate. This separation creates an electrical charge that will change value when the protected object is approached or touched by someone, creating, in turn, an alert.

These are motion detectors used to protect either rooms or corridors. They measure energy radiated by objects and thermal energy changes on the background of a scene is covered. On one side, this means that when a new source of energy, like a human, enters a space covered by the sensor, an alert is sent. Some sensors allow distinguishing between adults, child and pets. On the other, if a source of energy that was already present in the initial scene moves and covers the energy emitted by the objects in the background, an alert is also sent. Depending on the lenses of the passive infrared sensors, these will be suitable for covering short or long distances and wide or narrow field of views.

These sensors measure the variances between the emitted and received signal caused by the movement of any object within the energy field created. Because of their operating principle, they better detect motion that is either close or away from the sensor. One of the advantages and disadvantages of this type of sensors is that they can penetrate walls going outside of the desired area. While concrete might not be traversed and metal objects can cause irregular coverage, most plastics, glasses and other materials are penetrated.

These sensors detect the weight of a person or object when these pass over them. They usually present the shape of a mat but can also be placed under other objects.

There are some solutions in the market that combine more than one technology in a single sensor. The most common combinations are passive infrared and microwave sensors, or passive infrared and acoustic sensors.


The selection of an appropriate intrusion sensor can be kind of tricky, especially considering the wide variety of options available in the market. However, once you have acquired an overview of the different types of sensors, the choice should not be that difficult:

The suitable number and type of intrusion sensors to be installed depend mostly on the environmental conditions of your home. The floor in which you live, the size of the house, the number and positioning of the most sensible areas within your home and the design of the building itself are all characteristics to be considered when selecting the right combination of intrusion sensors.

Make sure that the intrusion sensors will adequately collaborate with the alarm system that you already have or that you plan to install. To enhance the communication between devices, it is advised to stay within a unique brand.

Intrusion sensors are usually battery-powered. They are easy to install and will remain available in case of an eventual power outage. In case you decide to buy them, make special attention to battery life. The number of intrusion sensors installed in a house can be quite high for which buying sensors with long-lasting batteries will reduce the level of maintenance required. For your information, intrusion sensors that use Bluetooth or other low-range communication protocols generally consume less energy than those using high-range communication protocols like Wi-Fi. Remember that all devices that are not directly connected to the internet will require a hub if you want to control them from remote.

Like with all internet-connected devices, it is essential to consider the distance between the intrusion sensors and the hub. Consider that the communication range specified by manufacturers correspond to ideal conditions, not taking into account the obstruction that walls may oppose.

This refers to the area that the intrusion sensor can monitor. Intrusion sensors with a greater field of view cover a wider area with, generally, a lower distance coverage. Cameras with a lower field of view cover a narrower area with, usually, a higher distance coverage. For instance, an intrusion sensor with a field of view of 130º may be able to cover a distance of about 7 metres, while an intrusion sensor with a field of view of 110º may be able to cover about 10 metres.

This refers to the capacity that some intrusion sensors have of distinguishing adults from pets, kids and other objects like vacuum robots. This will decrease the number of false alerts and avoid the activation of other automation rules like the turn-on of the lights when a pet passes by.

Some intrusion sensors can detect when someone is tampering them and informing you about it.

Some door and window sensors can be individually deactivated without the disarming the whole alarm system. This can be useful when you need to go out for a while, for instance, to take the dog for a walk.



Place the intrusion sensors in the different entry points of your home, in the passing areas like corridors and hallways that lead to the most sensible spaces and in any other sensible objects or object organisers like computers or drawers. When possible, avoid mounting the intrusion sensors on metal objects as some metals can affect the magnets within the sensors. If not possible, include some spacers made of low electrical conductivity materials like plastic between the surface and the sensors. Avoid also their exposure to sunlight and other heat sources. Take into consideration that the probability of detection of passive infrared and microwave sensors increase when placed in a way that the intruder walks parallel to them, not towards them. Microwave sensors should point away from metal objects that might cause partial coverage and mounted high close to the ceiling to increase the area covered.


Name each of the intrusion sensors that you install with a talking name like "Window Bedroom", "Medicine Cabinet" or "Hallway". This will enable you to know the exact source of threat in case that any activity is detected. Take some time to set-up the different automation rules that the intrusions sensors will trigger, either it is the turn-on of light or the turn off of the thermostat. If supported by the sensor, define the reset time, which is the time between the detection and activation of a device, like a light, and the deactivation of it. 


Make sure that the intrusion sensors are always in place and that there is not an object that can obstruct the detection of any movement inside and outside your home.


Intrusion sensors do not generally require any type of extraordinary maintenance except for wireless ones, which need a periodical replacement of the batteries. Keep the devices up to date with the last version of the software.


1,2 FBI: Uniform Crime Report, Burglary Offense Analysis Numbers and Percentage, 2016 - 2017. Accessed August 2019. <>.

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