Stream Emit Policy

AirLeak's BLE radio time-slices between scanning and the phone connection, and BLE notify bandwidth is finite. So the firmware does not stream a raw per-advertisement firehose. Instead it keeps a device-centric table and pushes a coalesced delta only when a device meaningfully changes. This page explains that emit policy (shouldEmit() in src/enrichment/device_aggregator.cpp, spec §7).

What triggers a delta

After the aggregator updates a device record, it emits a delta to the capture stream when any of these is true:

• New device, the MAC was just seen for the first time (always emitted).
• RSSI moved, the smoothed RSSI EMA moved by at least rssi_delta_emit dBm (default 6).
• New protocol bit, the device started broadcasting a BLE event type it hadn't before (e.g. it began emitting Find My frames).
• Tracked flag flipped, a tracked privacy flag changed (e.g. AirDrop went discoverable, Find My separated, random-MAC).
• Severity moved, the leakage score moved by at least sev_delta_emit (default 5).
• Heartbeat, the device is still present but unchanged for ~10 seconds, a liveness tick so the app's "last seen" stays fresh.

Everything else (e.g. yet another identical Nearby Info advertisement) just bumps last_seen and is coalesced away.

Both thresholds are tunable via config.set (rssi_delta_emit, sev_delta_emit), see Settings.

Coalescing and minimum interval

A short minimum-emit interval gate prevents a single jittery device from emitting many deltas back to back, changes inside that window are folded into the next delta. The 10-second heartbeat is exempt so liveness ticks are never suppressed. The streamer also dedups by MAC within each drain batch, so a burst collapses into one frame per device carrying the latest state.

The result: the phone sees a smooth, low-rate stream that still reflects every meaningful change, while the radio spends its time scanning rather than transmitting redundant notifications.

Wire format and self-healing

Deltas are length-prefixed CBOR frames with a sequence number. The app applies frames in sequence order; a gap (detected by a sequence discontinuity) triggers a capture.since backfill, and a ring wrap returns a fresh snapshot. If the device's delta ring overflows under backpressure it drops the oldest entry, bumps drop_count, and signals the app to re-capture.snapshot. So a dropped notification self-heals rather than corrupting the table. See State & Health Fields for the drop counters.

Fox Hunt exception

When you lock onto a device in the app's Hunt tab, the firmware sets a focus MAC that bypasses the emit gate for that one device, so its RSSI updates on every observation and the proximity gauge stays responsive. Clearing the lock restores normal coalescing.