What to expect. Best case — a quiet room, 4+ phones spread 2 m or more apart with line of sight — is roughly ±0.3–1 m. Hard floors and glass push that to a couple of meters; every result is drawn with its error radius, never as an exact pin. With only two microphones you get a curve ("somewhere along here"), not a point.

Ground rules. Media volume up and the silent switch off (the phones range each other with short beeps). Don't move a phone after marking it — moving one invalidates the calibration and the host must recalibrate. Keep the tab in the foreground while listening; backgrounding suspends the microphone.

Privacy. All audio is captured and analysed on each phone. The room relay only carries the floorplan (downscaled, if the host shares one), marker coordinates, beep timestamps and results — never sound. Nothing is stored on the server; the room evaporates when everyone leaves.