A Bluetooth Scan Gives You a Floor, Never a Count

A peripheral broadcasts advertising packets on three channels. Each packet carries a six-byte address, convenient as an identifier only if it stays still. Devices using resolvable private addresses rotate the value on an interval chosen by the manufacturer. The specification suggests keeping it under fifteen minutes.

One pair of glasses can therefore appear as several devices over an hour, while two signals cannot safely be treated as two pieces of hardware. A scanner count describes advertising identities in a window, not objects in a room. The two quantities should be reported separately.

The payload remains useful. Service UUIDs and manufacturer-specific data can distinguish a known product, turning detection into pattern matching against a list somebody maintains by hand.

That list can cover the recognizable end of the market. Coverage often follows the same few names, as in HackerNoon's piece on the Samsung and Meta rivalry, and their signatures are easier to identify. The harder problem is the unbranded long tail sold under a dozen marketplace names. Such devices may share firmware and advertise nothing that separates them from earbuds. They remain false negatives until somebody uses a sniffer and adds them.

Advertising behaviour can change with connection state, but NearLens has not confirmed one rule that applies to every tracked model. Connection state is therefore not a reliable proxy for whether a nearby device is active.

Signal strength does not solve this. A body between two radios costs more than several metres of open air, leaving proximity readings uncertain in crowded rooms. A tool should not render a confident zero. Reporting nothing detected is accurate. Reporting nobody nearby asks more of the radio than it can support.

The observation window adds another limit. A scan samples advertisements during a period, while a device can change state before or after it. Repeating a scan may improve the chance of seeing a broadcaster, but it cannot create a complete inventory of devices or activity.

A minimum of observed compatible signals can support a request for clarification or a review of local rules. It cannot establish the number of wearers, anyone's identity or whether a camera or microphone was active at the time.