A warehouse supervisor showed me a graph that looked like a heartbeat on espresso. The RSSI from one Beacon was swinging forty decibels every few seconds, and his location engine was tossing assets into random rooms. We found four causes. Three of them were not the Beacon.
Batteries fade before they die
A sagging coin cell is the easiest to miss. As voltage drops, transmit power drifts and the received signal slips a few decibels before the unit ever goes dark. We caught one at ten decibels below its healthy baseline two weeks before it failed. Replace on a schedule, not on failure, and this swing vanishes.
Bodies get in the way
A person walking between the Beacon and the gateway absorbs and reflects the signal. One body is three to five decibels of shadow; a forklift is more. If your RSSI only jumps when people move, that’s physics, not a fault. You fix it by averaging over a few seconds, not by swapping hardware.
Multipath is the quiet one
Hard surfaces bounce the signal, so the gateway hears a direct path and a delayed copy that lands on top of it. In a steel room that can add or cancel ten decibels depending on where you stand. This is why a Beacon flat against a girder reads worse than the same unit two meters out in open air. Move it off the metal and the jump settles.
Cheap gateways sample badly
Some gateways report RSSI faster than they measure it, so you see noise that isn’t there. We swapped one brand for another and the ‘fluctuation’ dropped by half with the Beacon untouched. If every unit looks jittery at once, blame the receiver before the transmitter.
What fixed the warehouse
We swapped the dying batteries, moved three units off the steel beams, and set the engine to average over five seconds. The heartbeat flattened. The Beacon had been fine the whole time. The graph was reporting the environment, the power, and the gateway, in that order.
What I check first now
Battery voltage. Then is it near metal. Then is everything jumping or just one unit. Then the gateway firmware. In that order. Nine times out of ten the Beacon is the last thing wrong, not the first, which is annoying because it’s the thing everyone points at first.
