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Most false presence detections are corrected by fixing the sensor’s geometry before changing its sensitivity. In the Shelly web interface, select the mounting position that matches the room map, enter the actual mounting height, set useful minimum and maximum detection heights, and run tilt calibration after mounting. Then reduce transmission power for a small room, lower detection sensitivity, raise the SNR threshold in small increments, and draw blind zones over furniture, doorways, windows, or adjoining spaces that should not count.
Make one change at a time while watching the live map and testing the room both occupied and empty. Recognition, velocity, and state-timing thresholds can suppress remaining noise, but setting them too aggressively can make the sensor miss a slow or stationary person.
What causes false presence detections?
The Presence Gen4 is intended to track presence rather than merely report a brief movement event. That means it can continue reporting a person who is sitting still, but it also means reflections and returns outside the intended room can be interpreted as an occupant. False detections usually come from one of four mismatches:
- The configured room does not match the installation. A wrong left, center, or right mounting choice, an incorrect height, or an uncalibrated tilt changes the area represented by the room map.
- The sensing field is larger than the room. Excess transmission power can let the sensor see through an opening or into an adjacent space.
- Background returns look like objects. Furniture, glass, windows, doors, and other reflective surfaces can produce signals that need stricter signal-to-noise or recognition thresholds.
- The state logic is too eager. Activation, release, tracking-loss, stillness, and timeout values determine how quickly a detection changes state. Short or permissive timing can make the reported state flicker.
Treat the live map as a diagnostic view. If activity appears in a neighboring room, a doorway, or a fixed piece of furniture while the room is empty, correct coverage and exclusions first. Threshold changes are most effective after the physical model is accurate.
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Start with the physical installation
Software cannot reliably compensate for a room map that describes a different installation. Perform these checks before tuning sensitivity.
Choose the correct mounting position
In the Shelly web interface, choose Left, Center, or Right according to where the sensor is mounted relative to the room layout shown by the interface. Do not choose the position that looks aesthetically centered on a wall; choose the position that matches the map’s coordinate system. A left-mounted device configured as center can shift the entire coverage area and place neighboring objects inside the monitored region.
If you move the sensor later, change this setting again. The position setting describes the room geometry; it is not a sensitivity control.
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Enter the actual mounting height
Measure from the floor to the sensor’s sensing position and enter that value rather than an estimate. A height error changes the vertical projection of the monitored area and can make floor-level or high-level returns appear in the wrong place.
Set minimum and maximum detection heights
Use the minimum and maximum detection-height fields to define the vertical slice that matters in your room. Raise the minimum when floor-level activity, low furniture, or pets are irrelevant to the automation. Lower the maximum when ceiling-level structures or reflections should not be considered. Keep the range wide enough to include the parts of a person you need to detect; overly narrow limits can remove legitimate occupants.
Run tilt calibration after mounting
After the sensor is physically fixed in its final position, run its tilt-calibration action. Shelly’s API documentation states: “For proper operation this must be called after sensor mounting.” Calibrating before installation, then changing the angle, leaves the device using the wrong orientation. Repeat calibration whenever you remount or noticeably alter the angle.
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Reduce the sensing field before tightening detection rules
Lower transmission power for a small room
Transmission power affects detection distance. If the live map shows returns beyond the room, reduce power one step at a time and observe whether the unwanted area disappears while the intended seating, desk, or walking area remains covered.
Use the lowest setting that still covers the room reliably. A power level that is appropriate for a large open area can be excessive in a compact bedroom, office, or hallway. Do not use power reduction as a substitute for a blind zone when a particular object is inside the necessary range; power changes the whole field, whereas a blind zone removes a defined area.
Use blind zones for known problem areas
Blind zones tell the Presence system to ignore specified areas during presence processing. Draw them over a doorway leading to another room, a window, a reflective cabinet, a television, or furniture that repeatedly appears as an object. The Presence API supports blind-zone arrays and room zones, and the web interface provides the corresponding room-area controls.
Make each blind zone no larger than necessary. A zone that covers an entire sofa may also remove a person sitting on that sofa, and a zone over a doorway can hide someone standing just inside the monitored room. After drawing a zone, test the boundary from several positions rather than assuming the map edge is exact.
Tune sensitivity and signal quality
Lower detection sensitivity
Detection sensitivity controls how readily the device accepts returns as presence. Shelly’s web-interface guide says that “low sensitivity reduces false triggers.” Start by lowering it one increment, then leave the room and watch the live map long enough to see whether the false object clears. Return to the room and verify that a person who sits still is still recognized.
High sensitivity is intended to improve detection of stationary objects. That can be useful in a room where someone may remain motionless, but it also makes marginal or reflective returns more likely to qualify. Use high sensitivity only when lower settings fail to hold a legitimate stationary occupant.
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Raise the SNR threshold gradually
The SNR threshold is the minimum signal strength required relative to background noise. Shelly describes higher values as improving stability and reducing false detections, while lower values react faster. Increase the threshold in small steps when the map shows unstable returns caused by weak or changing reflections.
After each increase, test three cases: an empty room, a person walking normally, and a person sitting or standing still. If the stationary test fails, reduce the threshold to the last reliable value. Do not raise it to the maximum simply because false detections are inconvenient; a stricter threshold can discard the weak returns that identify a real occupant.
Use recognition and velocity thresholds carefully
Object-recognition threshold
The object-recognition threshold is the minimum number of detected points required before the system recognizes an object. Raising it makes recognition stricter and can suppress small clusters of reflections. Increase it only after coverage, power, sensitivity, and SNR have been checked.
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Velocity threshold
The velocity threshold sets the minimum speed required for an object to qualify as detected. Raising it can ignore very slow movement and reduce activity from tiny or drifting returns. It can also miss a person who is standing still or moving slowly, so it is not a general-purpose “false positive” setting.
Change velocity only when the unwanted detections have a recognizable slow-motion pattern and stationary presence is not required, or when other settings have already preserved the required stationary behavior. Verify the result with a slow walk, a pause, and a normal walk.
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Stop presence-state flicker with timing thresholds
A physically clean map can still produce an unreliable automation if the reported state changes too quickly. Adjust timing thresholds incrementally and observe the actual state output, not just the visual map.
Motion activation
Motion-activation settings determine how much qualifying activity is needed before the sensor enters an active state. Increase the requirement when brief, isolated returns repeatedly turn an empty room on. Increasing it too far delays legitimate activation.
Motion release
Motion-release settings determine when the motion portion of the state is cleared after activity stops. A longer release can prevent rapid on-off cycles caused by intermittent returns, but it intentionally keeps the motion state active longer.
Tracking-loss
Tracking-loss thresholds control how long the system tolerates a missing or interrupted track before treating it as gone. Increase the tolerance when a person is briefly occluded by furniture or a doorway. Excessive tolerance can make a stale track remain after the person has left.
Stillness tracking
Stillness-tracking controls how the device handles an object that has stopped moving. If a seated occupant disappears too soon, increase the stillness-tracking allowance or use a less restrictive sensitivity and recognition combination. If a stationary reflection remains indefinitely, reduce the allowance after confirming that real occupants are still retained.
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Stillness timeout
Stillness-timeout determines how long a still track can persist before it is released. A longer timeout helps maintain presence for someone reading or sleeping; a shorter timeout clears a false stationary return sooner. Change it in small increments and test both a genuinely occupied room and an empty room containing the suspected reflector.
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A controlled tuning procedure
Use this sequence so that each adjustment has an observable effect. Record the previous value before changing it, especially if the sensor controls lights, heating, alarms, or access rules.
- Document the baseline. With the room empty, note where the live map shows objects and how the presence state behaves. Then test a normal walk, a stationary person, and the room’s most important boundary.
- Correct the room geometry. In the web interface, select the correct Left, Center, or Right mounting position, enter the measured mounting height, set minimum and maximum detection heights, and run tilt calibration after the final mounting adjustment.
- Remove excess range. Lower transmission power if the map extends beyond the room. Recheck the empty-room map before changing detection thresholds.
- Lower sensitivity. Reduce detection sensitivity one increment and verify that the unwanted return disappears without losing a stationary person.
- Increase SNR. Raise the SNR threshold gradually when weak or reflective returns remain unstable. Stop at the first setting that removes the false return while retaining the required occupant tests.
- Apply a blind zone. Draw the smallest zone that covers a known reflector or adjacent area. Test immediately inside and outside the zone.
- Adjust recognition or velocity. Raise the object-recognition threshold or velocity threshold only when the remaining false return fits that specific failure pattern. Recheck slow and stationary occupants after every change.
- Stabilize state timing. Tune motion activation, motion release, tracking-loss, stillness-tracking, and stillness-timeout values one at a time if the state flickers even though the map is clean.
- Validate the automation. Test empty, walking, seated, partially occluded, and boundary positions at different times. Restore the last value if a required case fails.
Common symptoms and the setting to investigate
| Symptom | First checks | Likely adjustment | Trade-off |
|---|---|---|---|
| Presence appears in the next room | Mounting position, mounting height, tilt, and live-map extent | Lower transmission power; add a blind zone over the opening | Too little range can leave the intended room uncovered |
| A fixed cabinet, window, or appliance is shown as a person | Whether the return is always in the same location | Lower sensitivity, raise SNR, or add a tightly drawn blind zone | Higher thresholds can hide weak legitimate occupants |
| Short flashes occur in an empty room | Background returns and state activation behavior | Lower sensitivity; raise SNR; increase motion activation modestly | Activation becomes slower |
| A seated person disappears | Sensitivity, recognition threshold, velocity threshold, and stillness settings | Use higher sensitivity or lower recognition/velocity strictness; extend stillness tracking or timeout | False stationary returns may last longer |
| The state rapidly alternates on and off | Tracking continuity and release timing | Adjust motion release, tracking-loss, or stillness timeout incrementally | The reported state may remain active after departure |
| Detection is missing near the floor or ceiling | Minimum and maximum detection heights | Widen the vertical limits to include the required area | Irrelevant floor-level or ceiling-level returns may reappear |
| Coverage is shifted from the room shown in the map | Left/Center/Right selection, measured height, and tilt calibration | Correct the position and height, then recalibrate after mounting | Changing geometry may require retesting all zones |
Settings reference
| Setting | What it controls | Use for false detections | What can go wrong |
|---|---|---|---|
| Detection sensitivity | How readily returns qualify as detected presence | Lower it to reduce false triggers | Stationary people may be missed |
| SNR threshold | Minimum signal strength compared with background noise | Raise it to improve stability and reduce weak-return detections | Fast or weak legitimate returns may be rejected |
| Object-recognition threshold | Minimum detected points needed to recognize an object | Raise it to reject small reflection clusters | Partially occluded or edge-of-room people may disappear |
| Velocity threshold | Minimum speed required for object detection | Raise it to ignore very slow returns when appropriate | Slow movement and stationary occupants may be missed |
| Transmission power | Detection distance | Lower it when the field extends beyond the room | Required areas may fall outside coverage |
| Minimum/maximum detection height | Vertical detection bounds | Exclude irrelevant floor- or ceiling-level activity | People outside the selected height range are ignored |
| Mounting position | Left, center, or right room placement used to configure coverage | Match it to the physical installation | A wrong choice shifts the modeled coverage |
| Sensor tilt | Device orientation relative to the room | Run calibration after mounting | Uncalibrated tilt misaligns the room map |
| Blind zones | Areas excluded from presence processing | Cover known reflectors and adjacent areas precisely | A person inside the zone will not be counted |
| State thresholds | Activation, release, tracking-loss, stillness-tracking, and stillness-timeout behavior | Use them to stop flicker after the map and signal are correct | State changes can be delayed or held too long |
Presence Gen4 and BLU Motion are different sensors
Shelly Presence Gen4 uses presence tracking intended to keep recognizing an occupant who remains still. Shelly BLU Motion is a separate Bluetooth motion sensor. They should not be tuned as though they have the same sensing model.
| Characteristic | Presence Gen4 | BLU Motion |
|---|---|---|
| Sensing approach | Presence tracking with object and signal thresholds | Bluetooth motion sensing |
| False-trigger controls | SNR, sensitivity, velocity, recognition, blind zones, and state thresholds | Motion sensitivity and blind-time behavior |
| Stationary occupants | Designed to continue tracking them when configured correctly | Reports motion events rather than the same continuous presence model |
| Room coverage | Configured with mounting geometry, heights, power, and zones | Separate placement and motion-coverage considerations apply |
If the requirement is “keep the room occupied while someone sits still,” evaluate the Presence Gen4 settings above rather than applying Bluetooth motion-sensor assumptions.
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Limits of what the settings can prove
No independently published false-detection rate or accuracy percentage is established in the official material used for these settings. A particular room’s result depends on mounting geometry, surfaces, furniture, openings, and the behavior the automation needs to recognize. Treat every threshold as a room-specific control and validate it with the actual people, objects, and boundaries that matter.
Do not declare the problem solved because the map is quiet for a few seconds. Check the room empty for a meaningful period, repeat the test after doors and windows change position, and test the occupancy patterns that triggered the original complaint. Keep a short change log of each setting and the observed result so that a later adjustment can be reversed without guessing.
When to stop tightening thresholds
Stop increasing strictness when false detections have disappeared and all required occupancy cases still work. Further increases can reduce responsiveness without providing a visible benefit. If a false return survives geometry correction, lower power, lower sensitivity, a higher SNR threshold, and a precise blind zone, inspect the physical scene for a moving source or reflection rather than continuing to raise every threshold.
The reliable order is physical alignment, coverage control, signal-quality tuning, spatial exclusion, and finally state timing. That order preserves the sensor’s ability to recognize a real person while removing the specific conditions that make an empty room look occupied.
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