Thread radios use the same crowded 2.4 GHz neighborhood as Wi-Fi and Zigbee, but at lower power. Concrete, rebar, and foil-backed insulation eat link margin fast. Link Quality Indicator (LQI) drops in diagnostics mean parent links are marginal — devices may still work until they do not, usually at night when sleepy children re-parent.

Low LQI through one wall is physics, not a defective sensor. The fix is topology, not cranking hidden transmit power.

Read LQI without obsessing over numbers

Vendor apps expose LQI or parent RSSI differently. Compare relative change: a sensor that dropped from strong to weak after a furniture move or new metal door tells you more than chasing a magic threshold.

Symptoms of concrete-related LQI pain: garage sensors fine when the door is open, flaky when closed; basement devices offline while upstairs routers look healthy; new unresponsiveness after kitchen renovation with metal studs.

Improve the mesh physically

Add a mains-powered Thread router on each side of the problem wall — a HomePod mini in the hallway, a Thread plug in the garage, an Eve extenders where supported. Sleepy devices should not be the only hop across concrete.

Move border routers out of cabinets and away from appliances that spew 2.4 GHz noise.

Avoid placing the only border router in the far corner of the home when sensors live on the opposite side of the foundation.

For detached structures, plan a dedicated border router in that structure instead of hoping through exterior concrete.

Software and channel hygiene

Align Zigbee and Thread channel choices where you control them — severe overlap lowers effective LQI without moving walls.

Update router firmware; some releases improve mesh reselection when LQI craters.

Remove ghost devices that keep radios polling weak parents.

Do not expect phone Wi-Fi speed tests to predict Thread through floors — measure with the sensor’s parent info instead.

When low LQI is acceptable

A contact sensor that reports once per hour with stable automations may live at moderate LQI forever. Chase fixes when you see missed events or battery drain from reattach loops.

Verify LQI improvements

After adding a repeater, check parent changes in the OEM app for problem sensors. Trigger automations ten times through the wall that used to fail. LQI work is done when parents stay on the near side of the concrete and events stop dropping.

Official sources