1. What "sensitivity" actually means in a walk through metal detector
Sensitivity is the gate's ability to detect a metal object of a given mass at any position as a person walks through. It is expressed in sensitivity levels (usually 1–9, sometimes 1–99 or 0–200 on industrial models) — a higher level detects smaller metal objects but also increases false alarms from coins, belts and phones.
The real measure of quality is not the maximum level but the usable range: a good gate detects a standard test piece (e.g. a 0.5g or 1.0g metal sample) reliably at high levels while remaining stable against interference. Certification standards like GB15210 define the required detection performance and test procedures.
2. Detection zones: why 33 zones beat 6 zones
Detection zones divide the gate's tunnel into horizontal layers. A 6-zone gate tells you something metal was detected and roughly where; a 18–33 zone gate pinpoints the exact height — chest, waist, ankle — which lets the guard search the right spot instantly without a full pat-down.
Zone count affects both price and performance: more zones mean more coils, more electronics and more precise localization, which is why airports and courts specify 18–33 zone gates while schools and events often use 6–12 zone models. For high-throughput screening, precise zone information dramatically improves search efficiency.
3. Sensitivity levels 1–9: how to choose the right setting
As a practical starting point: level 3–4 for general commercial use (schools, offices) — detects weapons-grade metal while tolerating phones and keys; level 5–6 for courthouses and government buildings; level 7–9 for airports and high-security perimeters where even small blades must be caught.
The correct setting is not the highest one: excessive sensitivity creates alarm fatigue, and guards who hear constant false alarms stop paying attention — the exact opposite of security. Set the level based on your threat profile and environment, then verify with test pieces at each setting.
4. The standards behind detection performance
In China, walk through metal detectors must meet GB15210 — the national standard for security inspection metal detection gates, which specifies detection sensitivity, zones, false alarm rates and environmental stability. Export models are typically certified to CE, FCC and country-specific standards such as NIJ in the US.
When buying, ask for the certification test report and check what test piece size the gate is certified to detect at each zone position. A certified gate with a documented test report gives you defensible screening performance — and matters in litigation if a failure is ever challenged.
5. Environment and interference: why a gate goes unstable
Walk through metal detectors are electromagnetic devices — nearby elevators, transformers, fluorescent lighting and moving metal doors all create interference that raises false alarm rates. Quality gates include multi-frequency and digital filtering to reject interference; some offer automatic calibration at installation.
If a gate becomes unstable, first check the environment, not the hardware: move it away from metal doors and power transformers, ensure the lane is clear of stacked metal objects, and rerun the calibration routine. Anti-interference design is a major price driver — cheaper gates are more sensitive to their surroundings.
6. Configuring your gate for the real world: a practical checklist
Installation: place the gate on a level floor away from metal interference, at least 50cm from walls and 2m from large moving metal objects. Power: use a stable supply; avoid sharing circuits with elevators or heavy machinery. Calibration: run the factory calibration after installation and after any relocation.
Operation: set sensitivity per your threat profile, define search procedures for the zone indicated by the alarm, and review false alarm statistics weekly — if alarms are excessive, adjust rather than disable. Our factory provides remote configuration support and training with every walk through metal detector order.
