Why garden zoning improves alarm reliability
A zone is a logical area that triggers a specific alert. In gardens, zoning reduces nuisance triggers by separating high-traffic pathways from low-traffic beds. If your perimeter is 40 m and your usable sensor range is 10 m, a practical baseline is about 2 zones (40 ÷ 20). This calculator then scales zones using risk and exposure inputs.
Coverage math behind sensor count
Sensor coverage is estimated as a sector: pi × range² × (angle ÷ 360). A 10 m sensor at 90 degrees covers about 78.54 m2. With overlap at 20%, needed coverage becomes area × 1.20, so a 96 m2 garden targets roughly 115.2 m2 of effective coverage. The tool converts this to a recommended sensor quantity, then suggests spacing along the perimeter.
Risk and exposure translate into zone density
Risk level increases redundancy where theft or animal intrusion is more likely. Exposure reflects openness, gaps, and unlit boundaries. For example, at 70% exposure the calculator applies a stronger scaling factor than at 30% exposure, increasing zones so each segment becomes shorter and faster to locate when a trigger occurs.
Tuning overlap and trigger hold for fewer false alerts
Overlap improves confirmation by letting two devices see the same approach line, but it can also increase sensitivity if aimed poorly. Trigger hold adds time filtering. A 4 second hold is often enough to ignore quick motions from leaves or small pets. The estimated false-alert reduction combines overlap, hold time, and a night-only schedule bonus.
Operational tips for real installations
Use realistic ranges based on walk-tests, not maximum specs. Avoid pointing sensors at sprinklers, reflective surfaces, or moving foliage. Keep cameras on entrances and gates, and use contact switches on shed doors. After calculating, label each zone by location, test at dusk, then adjust angles and spacing until triggers map cleanly to a single segment.