Quick Presets
Formula Used
Theoretical sector coverage: A = ½ × r² × θ, where θ is measured in radians.
Effective single-sensor coverage: Aeffective = A × technology × movement × sensitivity × environment × obstruction × safety factors.
Recommended quantity: N = ceiling[room area ÷ (effective sensor area × planning factor)].
Blind area: room area − estimated unique coverage. The calculator applies simplified planning factors instead of full ray tracing.
How to Use This Calculator
- Choose the area shape, units, dimensions, floors, and zones.
- Select a sensor technology or enter custom range and field-of-view values.
- Set mounting height, tilt, target type, movement direction, and reliability.
- Add obstacles with coordinates, then select environmental interference conditions.
- Choose automatic quantity or test a fixed number of sensors.
- Enter equipment, labor, wiring, tax, and contingency costs.
- Calculate, review warnings, drag sensor markers, and submit again when needed.
- Export the result as CSV, JSON, or a printable PDF report.
Sensor Technology Comparison
| Technology | Typical range | Typical view | Best use | Main caution |
|---|---|---|---|---|
| PIR | 8–15 m | 90–140° | Rooms, alarms, lighting | Thermal disturbances and direct approach |
| Microwave | 10–25 m | 100–180° | Large rooms and outdoor zones | May detect through light partitions |
| Ultrasonic | 6–12 m | Wide | Occupancy around partial obstructions | Air movement and acoustic reflections |
| Dual technology | 10–18 m | Wide | False-alarm reduction | Higher price and configuration effort |
| Millimeter-wave | 8–20 m | Configurable | Presence and subtle movement | Zone tuning and privacy considerations |
| Photoelectric beam | 20–100 m | Narrow line | Perimeters, gates, corridors | Alignment and physical blockage |
Example Data
| Scenario | Area | Technology | Range | Mounting | Target overlap |
|---|---|---|---|---|---|
| Small bedroom | 4 × 3 m | PIR | 8 m | 2.2 m wall | 10% |
| Office | 12 × 8 m | Dual technology | 12 m | 2.7 m ceiling | 15% |
| Warehouse aisle | 40 × 5 m | Microwave | 18 m | 3.5 m wall | 20% |
| Garden path | 25 × 4 m | Outdoor PIR | 12 m | 2.4 m pole | 15% |
| Parking area | 35 × 25 m | Millimeter-wave | 20 m | 4 m pole | 25% |
Motion Sensor Placement Guide
Good sensor placement begins with target movement, not only room size. A sensor may advertise a long range, yet walls, shelving, heat, weather, and mounting angle can reduce useful coverage. Cross-path movement usually produces stronger PIR detection because a moving person crosses several sensing zones. Direct movement toward the detector may create slower changes and delayed activation. Place sensors where normal travel paths intersect the detection pattern.
Mounting height changes both the near blind zone and the far ground reach. A sensor mounted too low can be blocked by furniture or vehicles. A sensor mounted too high may overshoot small targets or create weak coverage close to the wall. Use the manufacturer range as a starting point, then apply safety margins for real installations. High-security projects should include overlap at entrances, restricted areas, stairs, and valuable equipment.
Environmental conditions deserve separate attention. PIR devices can react poorly to direct sunlight, hot air, heaters, and rapid temperature changes. Microwave and radar devices may detect through lightweight materials or reflect from metal surfaces. Ultrasonic occupancy devices can be influenced by airflow and moving machinery. Outdoor units should have suitable weather protection, stable mounting, and masked zones that avoid roads, neighbors, trees, and pets.
The diagram in this tool offers planning guidance rather than manufacturer-certified detection mapping. Real sensors use multiple lobes, sensitivity rules, signal processing, and installation limits that simple geometry cannot reproduce perfectly. Verify every proposed location with product documentation and a walk test. Security, life-safety, accessibility, and code compliance should be reviewed by qualified professionals before final installation.
Frequently Asked Questions
How many motion sensors do I need?
The quantity depends on effective coverage, obstacles, target movement, overlap, mounting limits, and reliability. Use the recommended quantity as a planning estimate.
Where should a PIR sensor face?
Aim it across the expected path of movement. Avoid direct sunlight, heaters, moving curtains, strong airflow, and large windows.
Why is cross-path movement better?
Many PIR lenses create alternating detection zones. Crossing these zones produces stronger signal changes than moving directly toward the sensor.
Can one sensor cover an entire room?
Sometimes, but furniture, partitions, corners, and mounting geometry can leave blind spots. Large or complex areas usually need multiple sensors.
How much overlap is recommended?
General occupancy projects may use 10–20 percent. Higher-security designs often use more overlap around entrances, corners, and important assets.
Can microwave sensors detect through walls?
They may detect motion through lightweight partitions, glass, or thin materials. Sensitivity and zone boundaries should be tested carefully.
What mounting height should I use?
Follow the manufacturer specification. Common wall-mounted PIR sensors are often installed around 2.0–2.7 meters, but products vary.
Does the calculator replace a walk test?
No. A walk test confirms real detection performance after installation and should always be completed before commissioning.
Can I use this for outdoor security?
Yes, for early planning. Select weather exposure, suitable IP protection, obstruction loss, target type, and appropriate outdoor technology.