Choosing the wrong motion sensor for your property can mean false alarms at 3 a.m. or, worse, a real intrusion that goes completely undetected. The two dominant technologies — PIR and microwave — work in fundamentally different ways, and understanding those differences will save you money and frustration. Here's exactly what you need to know.
How PIR Motion Sensors Work
PIR stands for Passive Infrared. These sensors don't emit any signal — instead, they detect changes in infrared radiation (heat) within their field of view. When a warm body like a person or animal moves across the detection zone, the sensor registers the shift in heat signature and triggers an alert.
PIR sensors are split into detection zones using a Fresnel lens, which divides the coverage area into segments. Movement is detected when a heat source crosses from one segment to another — not simply when it stands still in the zone. This is important to understand: a person who stops moving directly in front of a PIR may not continue to trigger it.
Typical PIR specs to know:
- Detection range: 6–12 metres indoors (commercial-grade units can reach 15–20 m)
- Coverage angle: usually 90°–110° wide, some models offer 360° ceiling-mount versions
- Operating temperature: most are rated for 0°C to 40°C — extreme heat sources nearby can cause false alarms
- Response time: approximately 0.5–2 seconds after motion begins
PIR sensors are the most common choice for indoor residential and commercial security because they're affordable, reliable in controlled environments, and have low power consumption.
How Microwave Sensors Work
Microwave sensors are active — they continuously emit microwave pulses (typically in the 5.8 GHz or 10.525 GHz range) and measure the reflected signal using the Doppler effect. Any movement within the detection field changes the frequency of the returned signal, triggering the sensor.
Because microwaves can penetrate most non-metallic materials, these sensors can detect motion through walls, glass partitions, and even thin wooden doors. That penetration power is a double-edged sword: it makes them excellent for large open spaces and high-security applications, but it also means they can pick up movement from an adjacent room or outside traffic — leading to nuisance alerts if positioned poorly.
Typical microwave sensor specs to know:
- Detection range: up to 15–25 metres, with some industrial units reaching 60 m
- Coverage pattern: typically narrow and elongated (often described as a "curtain" pattern)
- Works in complete darkness — no thermal signature required
- More expensive than PIR equivalents at similar range
Key Differences at a Glance
| Feature | PIR | Microwave | |---|---|---| | Technology | Passive (heat detection) | Active (radio pulse + Doppler) | | Works through walls? | No | Yes | | False alarm risk | Heat sources, sunlight | Vibrations, nearby traffic | | Power use | Low | Moderate–High | | Best environment | Indoor, climate-controlled | Large spaces, harsh conditions | | Typical cost | $20–$150 per unit | $80–$400+ per unit |
Which One Should You Actually Choose?
The answer depends on your environment and threat model.
Go with PIR if you:
- Need cost-effective coverage for standard indoor rooms
- Are securing a home, office, or retail space with stable temperatures
- Want simple integration with most alarm control panels (PIR is the industry default)
- Need long battery life for wireless installations
Go with microwave if you:
- Are securing a warehouse, car park, or large open industrial space
- Need detection in areas with extreme temperature fluctuations (e.g., cold storage, unheated outbuildings)
- Require detection through obscured areas like frosted glass partitions
- Are running a high-security application where penetrating detection is an asset, not a liability
The Dual-Technology Option
Many professional-grade sensors combine both technologies in a single unit. These dual-tech sensors require both PIR and microwave to trigger simultaneously before raising an alarm. The result is a dramatic reduction in false alarms — an important consideration for monitored alarm systems where each false call can incur fees from your monitoring station. Brands like Bosch, Honeywell, and Optex all produce reliable dual-tech units in the $100–$300 range.
Before You Buy or Install
A few practical steps before committing to any sensor:
- Map your space — sketch coverage zones and identify heat sources, HVAC vents, and windows that could cause false triggers for PIR
- Check your alarm panel compatibility — not all panels support microwave or dual-tech sensors without an additional module
- Consider tamper protection — look for sensors with anti-masking features if the installation is in a publicly accessible area
- Verify IP or IK ratings if the sensor will be installed outdoors or in a dusty environment
If you're comparing supplier quotes or need a vetted installer, Mercoly lets you find and compare trusted Intrusion & Motion Sensors providers in one place, so you're not relying on a single quote or an unknown contractor.
Start your comparison today and get the right sensor specified correctly from the outset.