The short answer
A PIR sensor detects the heat movement of a body using passive infrared; a dual-tech sensor combines PIR with microwave detection and only alarms when both agree. A standard PIR (passive infrared) detector senses the change in infrared heat as a person moves across its field of view — it is the most common motion sensor in homes, reliable and low cost. A dual-technology sensor adds a second method, usually microwave (which detects movement by reflected radio waves), and triggers only when both technologies sense an intrusion at the same time. This dual confirmation makes dual-tech far less prone to false alarms from heat sources, draughts or moving objects, which is why it suits difficult environments. For most rooms a quality PIR is fine; dual-tech earns its place where false alarms are a problem.
Both sense movement, but they confirm it differently. The sections below explain how each works, why dual-tech reduces false alarms, and where to use each.
PIR vs dual-tech
- PIRPassive infrared (body heat movement)
- Dual-techPIR + microwave, both must agree
- False alarmsDual-tech lower
- CostPIR cheaper; dual-tech dearer
- SuitsPIR most rooms; dual-tech tricky areas
How a PIR sensor works
A PIR (passive infrared) detector is 'passive' because it emits nothing — it simply senses the infrared (heat) radiating from objects. Its lens divides the room into zones, and when a warm body moves from one zone to another the detector registers a rapid change in infrared and triggers. PIRs are tuned to respond to the size, speed and heat signature of a person, and good ones include some processing to ignore minor fluctuations.
PIRs are the workhorse of domestic alarms: inexpensive, low-power (ideal for wireless), and effective in normal rooms. Their weakness is that anything that mimics a moving heat source can cause a false alarm — sunlight moving across a room, a radiator or heater, draughts carrying warm air, or a pet (covered by pet-immune designs). They can also struggle if pointed at a heat source or a window. In a typical, stable room a quality PIR is reliable and sufficient.
How dual-tech sensors reduce false alarms
A dual-technology detector pairs PIR with a second, different sensing method — usually microwave, which emits low-power radio waves and detects movement by the change in reflected signal (the Doppler effect). The clever part is the logic: the sensor only raises an alarm when both the PIR and the microwave element detect an intrusion at the same time. Because the two technologies are fooled by different things — PIR by heat, microwave by certain movement and materials — it is unlikely both will false-trigger simultaneously.
This dual confirmation makes dual-tech sensors markedly less prone to false alarms in difficult environments: rooms with sunlight, heaters, draughts, conservatories, or areas with moving objects. The trade-off is higher cost, slightly higher power draw (microwave is active), and the need to set it up correctly so genuine intrusions still trigger reliably. The table compares the two.
| Factor | PIR | Dual-tech (PIR + microwave) |
|---|---|---|
| Detection method | Infrared heat movement | Infrared plus microwave |
| Trigger logic | Single technology | Both must agree |
| False-alarm resistance | Good | Higher |
| Power use | Low | Higher (microwave active) |
| Cost | Lower | Higher |
| Ideal location | Normal rooms | Sunlit, draughty or tricky areas |
How standard PIR and dual-technology detectors compare in practice.
Which should you use where?
For most rooms in a typical home — hallways, landings, living rooms without strong heat sources — a quality PIR is reliable, cheaper and the standard choice. There is no need to pay for dual-tech everywhere. Pet-immune PIRs handle households with animals (covered separately).
Use a dual-tech sensor where false alarms are likely or have been a problem: conservatories and sunrooms with strong, moving sunlight; rooms with radiators, heaters or air movement; large open areas; or any location where a PIR keeps triggering without cause. Many installations mix the two — PIRs in straightforward rooms, dual-tech in the awkward ones — which balances cost against reliability. The deciding question is the environment: stable room, PIR; challenging room, dual-tech.
Placement and setup matter as much as the technology
Whichever type you choose, where and how a sensor is fitted determines how well it works. PIRs are usually mounted in a corner about two metres up, angled so an intruder crosses the detection zones rather than walking straight at the sensor — movement across the field of view triggers a PIR far more reliably than movement directly towards it. Detectors should not point at windows (sunlight and outside heat), at radiators, heaters or boilers, or directly above fires and ovens, all of which invite false triggers. Keeping the lens clear of curtains, tall furniture and foliage avoids blind spots where someone could move undetected.
Dual-tech sensors add a setup consideration because the microwave element can see through thin partitions such as stud walls and glass, detecting movement in the next room or outside. A dual-tech detector must therefore be positioned and its microwave range tuned so it does not pick up activity beyond the room it is meant to protect — otherwise the very confirmation logic that reduces false alarms can be undermined, or genuine intrusions in the target area can be missed. Good installers walk-test every detector after fitting, moving through the room to confirm it triggers where it should and stays quiet where it should not. For a self-installed system, doing your own walk-test in each arming mode is the single most useful check you can carry out, and it matters whichever detection technology you have chosen. Repeating the walk-test occasionally is worthwhile too, because furniture gets moved, rooms get rearranged, and a detector that had a clear view when it was fitted can end up partly blocked by a new sofa, shelf or pile of boxes. A two-minute check now and then confirms the coverage you paid for is still there.
Frequently asked questions
Does a dual-tech sensor stop all false alarms?
No, but it greatly reduces them. Because it only alarms when both the infrared and microwave elements detect movement at once, the common single-technology false triggers — sunlight, heaters, draughts — are filtered out. Genuine simultaneous false triggers across both technologies are rare, though correct setup still matters.
Is microwave detection safe in the home?
Yes. The microwave element in a motion sensor emits very low-power radio waves, far below levels of concern, and is widely used in homes and businesses. It works by detecting the change in reflected signal as a person moves, similar in principle to automatic-door sensors.
Can a PIR see through walls or glass?
No. PIR detects infrared, which does not pass through ordinary walls or glass, so a standard PIR will not see movement outside a window. Microwave can penetrate some thin materials, which is one reason dual-tech sensors must be positioned and configured carefully to avoid detecting movement beyond the intended room.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property and system. They are guidance, not a quotation.