The serial number sticker contains a data matrix code (like a QR code). This encodes the following:
- Serial number
- A space character
- The mobile secret
For devices without BLE capabilities (Gen 2 devices), the data matrix only contains the serial number.
Note that older Photon, P1, Electron, and E-Series modules do not have a serial number sticker. Older Electron an E-Series with a "u-blox" sticker have the IMEI encoded in a 2D barcode. P0 modules (including the Photon) have an USI manufacturing code which is not easily mapped to any Particle identifier.