Radars

A radar counts people whether or not they are carrying anything. That is what makes it the only honest answer to "how many people are in this room" in a building where nobody wears a badge.

Two things catch people out. The wedge is thin directly underneath, so a radar over a desk sees the room better than it sees that desk. And glass is not a wall to a radar — a unit facing a glazed partition will count people in the corridor as though they were in the meeting room, which is why a room that is visibly empty can report two.

Mounting

Ceiling, centred on the area you care about. The sensing wedge spreads out below the unit, so it is thin directly underneath: a radar over one desk sees the whole room better than it sees that desk.

Mind the glass. Radar passes through glazed partitions. A unit facing a glass wall will count people in the corridor beyond as though they were in the room, and the symptom is a visibly empty meeting room reporting two. Either aim away from the glass, or draw the counted zone so that the corridor is outside it.

Record the mount height. Heights and the 3-D view are derived from it.

Nothing moving in view. A ceiling fan, a swinging door, a hanging banner in an airflow — anything that moves regularly is something a radar can decide to count.

Calibrating

A radar reports in its own coordinates. Calibration is what lines those up with the floor plan, so that "two people near the window" lands near the window.

Do it from the device's own page, and check it afterwards by having someone walk the room while you watch: the dot should track them. Five minutes of this is worth more than any amount of adjusting numbers.

Reading what it gives you

It counts people, not tags. That is the point, and it is why a radar zone and a tag zone are answering different questions even though the column is called the same thing.

The live feed is bursty. Frames arrive in pages rather than one tidy reading per second, so a count that jumps momentarily and settles is the feed, not the room.

Height is not what you would guess. The z figure a radar reports is not a person's height. Do not build anything on it.

When a radar is the wrong choice

You only need to know whether anyone is there. A presence sensor is cheaper and simpler.

You need to count people crossing a threshold, not standing in a room. That is a door counter, and the two numbers are not interchangeable.

The space is bigger than one unit covers. Two radars in one room need their overlap thinking about; two rooms with one each is usually the better layout.