FreeStyle Libre 2

Reverse engineering in progress.

Important device notes


Device Vendor ID Product ID
FreeStyle Libre 2 1a61 3950


This device uses the shared HID protocol used by other meters in the FreeStyle family, but introduces encryption.

Text commands are sent by the original software as message type 0x21, with responses as 0x60.


The commands sent to Libre 2 devices are encrypted. The encryption covers the 63 bytes remaining following the message type, for most of the message types used by the device, excluding the pre-initialisation commands (and their replies), the 0x22 keep-alive command, and the error replies.

The initialization appears to follow a handshake as follows: