Our product guides flag the distance and position outputs the same way every time: they are non-critical functions with limited accuracy. That sentence is often read as "ignore these fields". It means the opposite of what integrators need — these are the most useful numbers you have while installing the sensor, precisely because they are raw and unsmoothed.
This article is the method: what to subscribe to, what a healthy reading looks like, and how to decide between moving the sensor, changing a setting, or removing an interference source.
These values are diagnostic only. Do not build a product feature on them — the documentation is explicit that their accuracy is limited, and a customer-visible feature needs the primary outputs (presence, motion, fall state, breathing) instead.
What you can subscribe to
| Signal | Range / cadence | What it tells you |
|---|---|---|
| Human distance | 0–65535 cm, about every 2 s | Roughly how far the detected target is |
| Human position | x, y, z, about every 2 s | Where in the beam the target sits |
| Motion status | 0 none / 1 still / 2 active | Whether the target is moving at all |
| Body-movement level | 0–100 (5 s module, 1 s finished) | How much movement, in fixed bands |
| Approach / leave | 1–5, about every 2 s (presence module) | Direction of travel relative to the radar |
| Presence energy & threshold | fall radar, switchable | How strong the presence detection is firing |
The body-movement bands are worth memorising, because they turn a number into a sentence:
| Value | Meaning |
|---|---|
| 0 % | No person in range |
| 1 % | Still — breathing only, no limb movement |
| 2–30 % | Micro movement: small head or limb motion |
| 31–60 % | Walking or fast limb movement |
| 61–100 % | Running or large close-range movement |
A correctly aimed radar on a person lying still should sit at 1 %. That single number answers the most common installation question — "is it actually seeing the person?" — without any interpretation.
The method
1. Empty-room baseline
Before anyone is in the room, subscribe and watch for a minute. A healthy sensor in an empty room reports no target: distance absent, body movement at 0 %, motion status 0. If you see a distance, a position, or movement above 0 % with nobody present, you have interference — a fan, an air-conditioner motor, a curtain, or a reflective surface. Find it now, not after the customer calls.
2. Walk the room
Walk slowly from the door to the far wall, then back. Watch three things:
- The distance trace should rise and fall smoothly and end near the far wall's real distance.
- Body movement should read 31–60 % while walking and drop to 1 % when you stand still.
- Motion status should follow: 2 while walking, 1 while standing still.
If the distance stops changing while you keep walking, you have left the beam — that is your coverage edge.
3. Map the coverage edge
Repeat the walk along different paths and mark where the sensor stops reporting. Compare with the documented coverage for your variant: the finished presence radar covers roughly a 2.7 m radius; the 24 GHz presence module reaches about 12 m for a moving person, 6 m for someone sitting, 3 m for a sleeping person; the sleep radar's breathing detection degrades beyond about 1.5 m and disappears before presence detection does.
If the edge is short of where people actually are, that is a mounting or scene-mode problem, not a fault.
4. Verify the aim
For a bed installation, the beam must hit the chest, not the wall: the sleep radar is side-wall mounted at 1.8–2.2 m, or above the bed head tilted 30°–45°, with 45° recommended. Position x/y/z and the body-movement value together tell you whether you got it right — a target that only ever reports 1 % at the edge of the range is a target you are barely seeing.
5. Confirm the empty transition
Leave the room and time it. Declaring a room empty takes about 40 s of confirmed absence, by design; declaring it occupied takes under 0.5 s. If your "empty" transition is much faster, something is being missed.
Red flags and what they usually mean
| What you see | Likely cause | First move |
|---|---|---|
| Target reported in an empty room | Fan, AC motor, curtain, pet, reflective metal | Remove or re-aim away from the source |
| Distance jumps around with nobody moving | Multipath from a metal surface or a second radar | Check line of sight; see ghost targets |
| Distance pinned at a round number (0 or max) | Out of range or field saturated | Move the sensor closer / reduce range |
| Body movement never drops below 30 % | Beam too wide for the room, or interference | Use a smaller scene mode; lower sensitivity |
| Still person reads 0 % | Beam missing the chest, or sensitivity too low | Re-aim; raise sensitivity one step |
| Readings change over weeks with nothing moved | Position drift — new furniture, hanging objects | See radar position drift |
Decide in this order
- Can I remove the interference? Cheapest fix. Fans and air-conditioner motors in the beam cause most false readings.
- Can I move the sensor? Coverage that misses the occupied area is usually a position problem.
- Can I shrink the range? The smallest scene mode that still covers the room is the most effective single change — the mode table is in the presence radar guide.
- Only then change sensitivity. One step at a time, and note the change. Higher sensitivity catches micro-movement and also picks up curtains and fans.
- Room-size adjustment. Below about 15 m², drop sensitivity one step; above about 40 m², raise it one step — small rooms strengthen reflections, large rooms weaken them.
Keep the baseline
Save the empty-room reading and the walk-through trace for every installation. It is the only objective record of what the sensor saw on day one, and it turns "it worked when you left" into a comparison you can actually make.
Where to go next
- The fields in full: presence radar guide, sleep radar guide, fall radar guide
- Why it behaves this way: How mmWave Radar Works and Radar Latency Explained
- Setting expectations on the numbers: Three mmWave Radar Specs That Are Almost Always Exaggerated
- Mounting geometry: Sleep Radar Mounting Position
- Multiple radars in one home: Running Several Radars in One Home
Finished radars and modules are on Tindie.
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