What are volumetric motion sensors, and how do they work?
Volumetric detectors are advanced motion sensors designed to detect intruder movement within the interior of a protected space — the core of full 3D protection in professional alarm systems for homes and businesses.
Motion sensors respond to changes within a defined area, such as shifts in infrared energy or in a reflected signal, caused by something moving.
They use infrared (PIR), microwave, or ultrasonic technologies to sense movement and energy changes in real time.
When the alarm is armed, the sensor reports what it detects to the control panel, which applies the system's settings to decide whether to raise an alarm.
Which detectors are active depends on the alarm mode you choose, for example fully armed when you're out or partially armed at night. Professionally monitored alarms are backed by a monitoring centre that's staffed 24/7.
How a volumetric motion sensor works
A volumetric motion sensor monitors a three-dimensional space — a volume — for changes in infrared energy or reflected signals caused by movement, so it can detect a possible intrusion in real time. Unlike sensors that protect a single door or window, it protects the space itself: when the alarm is armed, movement through its detection zones can trigger an alert. How reliably it detects depends on the sensor technology, its coverage pattern and sensitivity, the direction of movement, the environment and how the system is set up. Pet-friendly settings may also deliberately ignore some smaller movements.
01 — Detection
Movement is sensed
The sensor picks up a change within its coverage area, such as a shift in infrared energy as a warm body moves from one detection zone to the next.
02 — Signal
Signal transmission
The sensor immediately sends a signal to the central alarm control panel.
03 — Verification
Signal is assessed
The control panel processes the signal and applies the alarm's configured settings. On professionally monitored systems, the monitoring centre then checks whether it's a genuine intrusion or a false alarm.
04 — Response
System responds
If confirmed: an audible siren, a mobile app alert, and, where applicable, a monitoring centre response.
With the alarm armed, the sensor watches layered detection zones across the room. As a warm body moves from one zone to the next, the change in infrared energy creates a signal spike. The central unit processes the signal, the monitoring centre checks it, and the siren keypad responds.
Core components of a volumetric detector
A volumetric detector senses movement within a defined zone using infrared or microwave signals. It doesn't rely on contact or pressure — it picks up on changes in energy patterns, allowing it to "see" movement through invisible waves.
PIR sensor
Passive infrared
Doesn't detect heat or movement directly. It measures changes in infrared radiation across its field of view as a warmer (or cooler) object, such as a person, moves between its detection zones.
Microwave
Active RF sensing
Emits microwave signals that bounce off surfaces to monitor a defined area. When movement disturbs the energy field, the detector is activated.
Dual-technology
PIR + microwave
Combines PIR and microwave sensing for improved accuracy. Typically both technologies must register a disturbance before an alarm is raised, which helps reduce false alerts.
Ultrasonic
High-frequency sound
Sends high-frequency sound waves and measures the return signal. When an intruder disturbs the wave pattern, the system detects the variation.
The purpose of a volumetric detector
Volumetric detectors monitor an area for changes in energy that signal movement or disturbance. The size of the protected zone depends on the sensor's range and placement — if it detects motion, heat, or electromagnetic changes, it flags a possible intrusion.
If the alarm is armed and the system registers an intrusion, a siren can sound to scare the intruder away and alert homeowners. Where the alarm is connected to a remote monitoring service, operators immediately check whether it is a genuine intrusion — not a false alarm — before calling law enforcement.
Active and passive volumetric sensors
Home motion sensors are becoming increasingly sophisticated, with many now using volumetric technologies. These devices are classified by how they sense motion.
Active
Emits energy to detect disruption
Active sensors emit energy into a defined area to monitor for disruptions or changes in the pattern. Movement alters the signal being received, triggering the system — ideal for detecting subtle motion across large spaces.
Microwave volumetric detectors
Generate continuous microwave waves filling a detection zone. Highly sensitive to distance, speed and direction, and effective near heat sources or ventilation, where infrared can struggle. Typically installed by professionals for correct range and angle.
Ultrasonic volumetric detectors
Emit high-frequency sound waves and measure the time taken to return. Particularly useful in controlled indoor spaces where accuracy and sensitivity matter most.
Passive
Reads energy already present
Passive volumetric sensors don't emit signals into the space. Instead, they detect energy naturally emitted by an intruder or object within the protected area — often less susceptible to interference or tampering, and a discreet, reliable layer of security.
PIR sensor (passive infrared)
Measures changes in infrared radiation across its field of view. When a warmer or cooler object, such as a person, moves from one detection zone to another, the change in infrared levels can trigger an alarm. Many PIR sensors offer pet-friendly settings designed to ignore some smaller movements, such as pets below a certain weight, to reduce false alarms.
Outdoor volumetric detectors
Outdoor detectors often combine infrared and microwave technologies for maximum accuracy and reliability, since there are more external stimuli likely to trigger the alarm — garden animals, temperature shifts, foliage moving in the wind.
Where they're installed
Around gardens, driveways, and entrances
Creating a virtual perimeter barrier around the property
Alongside existing door, window, and camera coverage
What happens on trigger
Deterrents such as flashing lights or sirens activate
Direct alerts are sent to a monitoring centre
Intruders can be deterred before they reach entry points
PIR sensor vs. volumetric detector
When it comes to home motion sensors, the same terms are often used interchangeably by different security providers and advice sites — here's the distinction.
Term
Also known as
What it is
PIR sensor
Infrared monitor sensor
A sensor that detects changes in infrared radiation as warmer or cooler objects, such as people, move across its detection zones. A PIR sensor can itself be one type of volumetric detector.
Volumetric detector
Volumetric detector
A security device that monitors an entire volume of protected space using a combination of technologies, such as PIR and microwave sensors together.
Where are motion sensors used?
Motion detection technology is versatile, and has been adopted in residential and commercial settings alike.
Inside homes and offices
Living rooms or open-plan spaces
Hallways and staircases
Garages or basements
Entryways and main corridors
Commercial & industrial
Restricted areas
Corridors or access-controlled zones
Large storage rooms or workshops
Open-plan production areas
The ideal approach — especially for offices — is to cover large volumes of space without needing numerous individual devices. Integrated with remote monitoring, these sensors let businesses protect premises even without personnel on-site.
What is a volumetric alarm system?
These sensors form a vital part of a volumetric alarm system, and may connect to door and window sensors or CCTV cameras for comprehensive intrusion detection. Systems typically cover a range of up to 12 metres, indoors or outdoors.
Component 01
Volumetric motion sensors
Pick up on movement within defined indoor or outdoor zones, using infrared, microwave, or dual-technology detection.
Component 02
Central control panel
The hub linking every device. It processes signals from the sensors and applies the alarm's configured settings, such as which detectors are active in the current alarm mode.
Component 03
Siren or strobe light
An audible and visual deterrent that activates as soon as the alarm is triggered.
Component 04
Mobile & remote monitoring
Sends an alert directly to your smartphone, or to a professional monitoring centre for independent verification.
Within a Verisure Smart Alarm System, these components work as an advanced, professionally monitored network — every alert verified by trained specialists who can trigger an emergency or guard response, ensuring immediate action if an intrusion occurs.
How much does a volumetric alarm cost?
Cost depends on several key factors — the level of integration with smart systems, the number of additional features, and the sensor technology used.
Sensor type
Choosing from PIR, microwave, or dual-technology sensors affects how expensive the system is.
Range & coverage angle
Higher-end sensors cover wider areas and provide more accurate detection across large or open-plan rooms.
Pet immunity
Some sensors are designed to ignore pets, reducing false alarms while maintaining reliable protection.
Smart integration
Connecting with smart home or app-controlled platforms allows remote monitoring and control.
Installation complexity
Professional installation ensures optimal positioning and calibration for effective detection.
While cost can vary, reliability and quality shouldn't be compromised — choose certified, professionally installed motion detectors that meet recognised safety and performance standards.
Advantages of motion sensors in home security
Their ability to sense movement within a full 3D space gives volumetric sensors a critical role in both domestic and commercial alarm systems.
01
Spot intruders before you see them — energy-change detection keeps you two steps ahead.
02
Wide coverage protects large areas with fewer devices, improving efficiency and cost.
03
Dual-technology monitoring cuts down false alarms and saves time and resources.
04
Easily integrated into smart systems — cameras, sirens, panels, door and window sensors.
05
Modern design means sensors are energy efficient, durable, and low maintenance.
06
Advanced models operate year-round, in all weathers, even low light and cold snaps.
Smart home security from Verisure
Every Verisure smart alarm system includes expertly installed cameras, motion detectors, and sensors, all connected to our 24/7 Alarm Receiving Centre. If your armed alarm is triggered, inside or outside your property, trained specialists verify the alert within seconds and can request emergency assistance if needed.
