When a gate alarms constantly, the equipment gets the blame. In practice, most of these alarms come from three places: a sensitivity setting that was never matched to the entrance, an installation environment that interferes with the gate, and the way people actually walk through it.

This is the order we work through on site — before anyone concludes that the detector is faulty.

1. First, Separate Real Alarms From Instability

These two problems look identical at the entrance and are solved in completely different ways:

• Real alarms. The gate alarms because someone is carrying metal above the threshold. The gate is doing its job — the sensitivity is simply set tighter than the site’s screening policy needs.
• Instability. The gate alarms with nobody passing, or alarms on the same person regardless of what they empty from their pockets. That is interference or a calibration problem, not a detection decision.

Tuning settings on an unstable gate only hides the problem. Fix the cause first.

2. Tune Sensitivity Per Zone, Not Globally

Detection zones do not see identical surroundings. A zone next to a handrail, a locker bank or a steel door behaves differently from the middle of the passage. Lowering the overall sensitivity to stop one zone from alarming weakens the rest of the gate.

• Adjust one zone at a time, and test with the same person and the same items each time.
• Use the gate’s own records — passage count and alarm count — rather than judging by impression during a busy morning.
• If the model offers preset application scenarios, start from the one closest to your site, then fine-tune individual zones.

3. Check the Installation Environment

This is the most common root cause, and the easiest to overlook because nothing visibly changes at the entrance.

• Metal-free area. Every model specifies a minimum metal-free horizontal distance around it. Compare that figure with what your entrance actually provides — walls, signage, door frames and floor structures all count.
• Moving metal. Rolling shutters, motorised gates, trolleys, escalators and vending machines cause alarms that appear random until you notice what is moving at the same moment.
• Fixed metal close to a pillar. Railings, pillars with steel reinforcement and metal-framed partitions affect the nearest zones most.
• What changed recently. A new railing, a new machine, a moved gate — anything new explains alarms that started on a specific date.

If alarms started on a particular day, ask what changed that day. The answer is usually in the building, not in the gate.

4. Look at How People Actually Walk Through

A gate reports what passes through it; it cannot know intent. Several habits generate avoidable alarms at peak times:

• Two people walking through side by side, so the gate cannot separate their signals.
• Students or staff hugging one pillar, which pushes the carried items into a single zone.
• Bags, umbrellas or instrument cases carried through instead of placed on the belt of the X-ray lane.
• A queue that compresses people into the passage so that the next person is already inside when the alarm sounds.

Passage discipline — one person at a time, bags handled separately — removes more false alarms than any setting change.

5. Coordinate Neighbouring Equipment and Frequency

Two or three gates standing side by side, plus an X-ray machine, turnstiles and door motors, form an electromagnetic environment. Digital filtering handles most of it, but the settings have to be planned:

• Do not leave adjacent units on the same operating frequency if the model allows frequency selection — separate them.
• Allow the recommended distance between gates and between a gate and the X-ray machine’s drive motor.
• Re-check the settings after any change to the layout, including adding a second gate.

6. Give Operators Something to Do With an Alarm

An alarm that is followed by nothing teaches staff to ignore the gate — and an ignored gate is a false-alarm problem that has turned into a security problem.

• Define the second check: who does it, with what handheld detector, and where the person steps aside so the queue keeps moving.
• Use different alarm tones for gates in the same area, so staff know which unit is calling.
• Review the alarm log monthly. If a zone accounts for most alarms, it needs attention before the staff stop reacting.

Symptom, cause and first check

Summary

Work through it in this order: confirm whether the alarms are real or instability, tune sensitivity zone by zone, check the installation environment, discipline the passage, plan the frequencies of neighbouring units, and give operators a defined second check. Most “faulty detectors” are resolved in the first three steps. If the gate is still unstable after all of them, that is when calibration or hardware support is genuinely needed.