Understanding how smart glasses use BLE broadcasts
Modern smart glasses and companion wearables stay connected to phones using Bluetooth Low Energy (BLE). They continually advertise short radio packets so a paired device can find them again. This article explains what those broadcasts contain, why they appear, and how Unrecorded uses them for situational awareness — not proof of active recording.
What BLE advertising is
BLE peripherals do not wait to be asked for their presence. They periodically transmit advertising packets — small bursts of data any nearby phone or scanner can receive without pairing. This is how wireless earbuds reconnect after you open their case, and how smart glasses stay available to a companion app.
From a privacy perspective, advertising means a wearable may leave visible traces in the radio environment: a name, a signal strength reading, and sometimes manufacturer or service identifiers. Those traces can suggest that hardware may be nearby. They do not reveal whether someone is recording video or audio right now.
What appears in a typical advertisement
When Unrecorded (or any BLE scanner) receives a packet, the operating system exposes a subset of fields. Not every device advertises every field, and values can be hidden or randomised by the manufacturer.
| Field | What it means | Privacy note |
|---|---|---|
| Local name | A human-readable label (for example a product or brand string) broadcast in the packet. | May be empty, generic, or changed by the user or firmware. |
| RSSI | Received signal strength — a rough hint that a transmitter is closer or farther, not an exact distance. | Noisy; walls and bodies affect readings. |
| Service UUIDs | Identifiers for Bluetooth services the device may offer when connected. | Often absent in advertising; not unique to recording. |
| Manufacturer data | A company ID plus optional payload defined by the vendor. | Can support pattern matching; not proof of a specific model. |
| Connectable flag | Whether the device is currently accepting connection requests. | Indicates availability, not recording state. |
Why wearables advertise continuously
Smart glasses and similar wearables need a reliable link to a phone for setup, firmware updates, media transfer, and companion-app features. BLE advertising supports:
- Initial pairing — your phone discovers the glasses during setup.
- Reconnection — after sleep or out-of-range events, the phone can find the device again.
- Companion-app sync — background services may look for known peripherals.
Advertising activity is normal for connected wearables. It is not the same as active video or audio capture. A device can advertise while idle, and it can record without advertising a recognisable name.
How Unrecorded observes signals
Unrecorded runs on your Android device and performs foreground BLE scans in short batches (roughly every 10–15 seconds while the app is open). Each batch yields a set of observations: names, signal strength, and other fields the OS exposes.
Those observations are merged in memory inside a
ScanSession — the app's session layer for tracking what
has been seen recently across scan batches. The session:
- Combines repeated sightings of the same nearby signal (smoothing noisy RSSI readings over time).
- Expires entries that have not been seen for a configurable stale period (about 60 seconds).
- Resets when you clear app data or uninstall — it is not persisted to disk as a history of people or addresses.
Unrecorded does not upload scan results to our servers. Processing stays on your device. The goal is a calm privacy-risk indicator based on what your phone can currently hear — not a log of everyone who passed nearby.
Pattern matching, not machine learning
Unrecorded uses rule-based classification in
packages/unrecorded_core. A local catalogue of known
hardware fingerprints — name keywords, cautious address-prefix hints,
and manufacturer IDs where documented — is compared against each
observation. Examples in the catalogue include patterns associated with
Meta / Ray-Ban, Snap Spectacles, Even Realities, and other wearable
lines.
Separately, a benign-device filter down-ranks common non-recording hardware so alerts are less noisy:
- Headphones and speakers (AirPods, Galaxy Buds, Bose, JBL, …)
- TVs and streaming devices (Roku, Chromecast, Fire TV, …)
- Keyboards, mice, and fitness bands
When several weak indicators align, the app may show a potential privacy risk level (low, medium, or high). That score reflects how closely visible signals match known patterns — not proof of recording.
Honest limits
Important: A signal that may match a smart-glasses pattern only means compatible hardware might be nearby. It is strictly an indicator of proximity and pattern similarity — not absolute proof of active video recording.
- Device names can be hidden, randomised, or spoofed — matching is probabilistic.
- RSSI fluctuates; “closer” on screen is an estimate, not a measured distance.
- Phones, body-worn cameras, and microphones without useful BLE advertising are outside this detection path.
- Unrecorded is a privacy awareness utility, not a security guarantee.
For a consumer-oriented guide to situational awareness in public spaces, see How to avoid being recorded by smart glasses: a practical guide.