How Smart Glasses Scanner works

1. Scan: what an iPhone can hear

Most wireless accessories, smart glasses included, announce themselves with short Bluetooth Low Energy (BLE) broadcasts called advertisements. Any Bluetooth receiver in range can pick up these broadcasts without pairing or connecting — the same mechanism that lets a phone list headphones to pair with. Three separate questions decide what a scanner can do with them: what the Bluetooth specification allows a device to broadcast, which of those fields iOS chooses to expose to an app, and what a particular product actually transmits in a given state. Only the first two are documented; the third has to be measured.

On iOS the app never sees the raw radio packet. Apple's Core Bluetooth framework delivers a small set of decoded fields per discovery: local name, manufacturer data, service data, service UUIDs, overflow service UUIDs, transmit power level, whether the device is connectable, and solicited service UUIDs. That is the entire list (Apple, Advertisement Data Retrieval Keys). There is no hardware address, and the identifier iOS assigns to a peripheral is app-specific and may change.

The app only listens. It does not connect to, pair with or transmit to any device, and Bluetooth observations stay on your iPhone.

2. Match: comparing against researched signatures

Each advertisement is normalised (the two-byte company identifier is read from the manufacturer data, 16-bit service UUIDs are canonicalised, names are trimmed) and compared with a catalogue of signatures. A signature is a small, data-driven description of what a device family is expected to broadcast: a company identifier, one or more service UUIDs, a name pattern, or a byte pattern inside the manufacturer payload.

Every signature carries its provenance: where the information came from, under what licence, whether we have confirmed it on hardware, and on which iOS versions. Today the catalogue holds identifiers registered with the Bluetooth SIG by manufacturers such as Meta Platforms Technologies, Snap and Even Realities, plus one community lead recorded so it can be tested. None has been confirmed by us yet; where signatures come from explains the rules and testing status shows what is pending.

3. Score: evidence that has to agree

A match produces a list of evidence items, each with a weight and a plain-language explanation. The confidence score combines them with a noisy-OR rule, so independent evidence compounds, and a structural cap keeps any single kind of evidence below the medium level. In practice:

• Company identifier alone: low. It may be a headset, a controller or something else from the same manufacturer.
• Company identifier plus a matching service UUID: medium, once hardware testing shows the combination is specific to glasses.
• Company identifier, service UUID and a name or payload pattern: high, again only once tested.

The weights are explicitly uncalibrated until we have measurements. The detection methodology page shows the formula, the default weights and worked examples.

4. Understand: what you see in a detection

A detection shows the device family the signature belongs to, the evidence that matched (with sources), the confidence level, a coarse signal category (very strong, strong, moderate, weak), and when the signal was first and last seen in this session. It never shows a distance, because signal strength is not distance, and it never comments on what the device is doing.

What "high confidence" means: with the current, uncalibrated weights, at least three independent kinds of evidence agreed, for example a company identifier, a service UUID and a name or payload pattern. It is a statement about how well the signal matched a signature, not about whether a camera is on, who is wearing the device, or how far away it is. Until a signature has been confirmed on real hardware, no real signal can reach this level.

Repeated sightings of the same peripheral are grouped into a session, which ends after two minutes of silence. If a device rotates its address it appears as a new session; sessions are not linked across rotations, because that would amount to tracking.

What runs in the background

Apple allows Bluetooth scanning in the background only under specific conditions: the app must scan for explicit service UUIDs, repeated discoveries are coalesced into one, the scan interval becomes slower, and the app can be terminated to free memory. Whether the glasses we study broadcast a service UUID that can serve as such a filter is unknown until tested. Any background feature will be described as best-effort, slower and able to miss devices. Read what iOS lets a Bluetooth scanner do.

Privacy by construction

The app has no account, never uses location, and never uploads Bluetooth observations; detection history stays on your iPhone and can be deleted in one tap. The full list of promises and how each one is enforced is on the privacy page.

Where to go next

• Explore device research — the record for each product, with statuses
• View testing status — the protocol and what will be published
• How to detect smart glasses — visual cues and Bluetooth, for people as well as apps
• FAQ — the short answers