Hardware: The second generation sensor has a different camera than the first generation.
Firmware: The second generation sensor comes with updated firmware (version 2.3) for more optimized mixing and as a result, a slight increase in test speed. The firmware updates that come in the second sensor is available to anyone on the first generation sensor by way of a firmware update via the Nima app. You can see your firmware version in the app.
Packaging: The second generation sensor comes in updated packaging.