Because phone detection is not a phone-recognition technology. The gate reacts to a specific electromagnetic or metal signature, and a bunch of keys, a steel-toe boot or a belt buckle can present a similar signature. When sensitivity is turned up to catch a phone hidden in a pocket, the gate also starts catching everything else. That is a configuration problem, not a machine fault.
Calibrate on an empty, clear passage first, then raise sensitivity zone by zone while a tester walks through with a phone in a pocket — not by turning the global dial to maximum. Move anything metal out of the doorway, keep the gate at least a metre from motors and cabling, and agree a routine: bags off the shoulder, phone out, walk through at normal pace. Most "false alarm" complaints disappear once those three things are done.
It can, and at high sensitivity it will. Sites that only care about phones usually accept a short list of "expected" alarms and train staff to ignore those.
On multi-zone gates yes, and it is the main tool for reducing nuisance alarms — set the pocket and bag zones higher, keep the feet zone lower.
No. Detection is based on the device's physical signature, so a switched-off phone is still found. That is why phone detectors are used in exam halls.
Check for a second device — a smart watch, a tablet in a bag, or a medical implant. If none, recalibrate; the baseline may have drifted after a nearby metal object was moved.
