Description
Probe-request sensing extracts presence and trajectory information from the unsolicited management frames Wi-Fi devices broadcast while scanning. Sniffers passively log (timestamp, MAC, SSID-list, RSSI) tuples and convert them into device counts, dwell times, and inter-area flow estimates. Despite MAC randomisation it remains a popular cheap modality for retail / event analytics, and is a useful BLE-side companion to probe-based ground truth in crowd studies.
When it's used
- Cheap mobile-device counting in indoor venues
- Crowd-flow inference from inter-AP MAC sightings
- Calibration ground truth for CSI-derived people counting
Limitations
- MAC randomisation degrades device-level continuity
- Counts devices, not people (carry-state, multi-device users)
- Privacy-sensitive — handling raw MACs is regulated (GDPR)