When someone lost their phone somewhere inside an office and the usual find-my tools weren't cutting it, they asked Claude for ideas. The suggestion: use Bluetooth signal strength (RSSI — Received Signal Strength Indicator) as a proximity sensor. Walk around with a laptop or second device, watch the RSSI value for your phone's Bluetooth identifier climb as you get closer, and triangulate the location by moving toward the strongest signal. It's low-tech, requires no extra apps, and works anywhere Bluetooth reaches.
The reason this works is straightforward. Bluetooth signal strength degrades predictably with distance and physical obstructions. A phone sitting in a desk drawer or slipped behind a cabinet cushion will still broadcast a Bluetooth beacon even when the screen is off and the ringer is silenced. RSSI won't give you centimeter precision, but it's accurate enough to identify the right room — or the right corner of a room.
On a Mac, you can scan for nearby Bluetooth devices using the Bluetooth Explorer tool inside Xcode's Additional Tools package, or use a free app like "Bluetooth Screen" to watch signal levels in real time. On Windows, apps like Bluetooth LE Scanner expose RSSI readings. Linux users can run hcitool lescan and bluetoothctl from the terminal. Android has several BLE scanner apps ("nRF Connect" is a reliable one). The phone needs to have Bluetooth enabled — which it almost always is by default.
The practical workflow: open your scanner, find your phone's Bluetooth device name or MAC address in the list, note the RSSI (typically displayed as a negative number — closer to zero means stronger signal, so -45 dBm is much closer than -85 dBm), then walk slowly through the space while watching the number. Move toward improving signal. Stop when it peaks.
This technique generalizes beyond lost phones. The same approach works for locating any Bluetooth peripheral — a misplaced tracker, a wireless headset, a BLE-enabled sensor in a server rack. It's also a useful mental model for anyone building indoor positioning features: RSSI-based proximity is a real, deployable tool, not just a theoretical one. The HN thread discussing this post surfaced additional refinements, including averaging multiple readings to reduce noise and using multiple scanning devices simultaneously for faster triangulation.