Intrigued I was too and just discovered the following:
A lot of the new Gx000 kit uses Garmin’s GRS 77 Attitude and Heading Reference System (AHRS). Combining inputs from GPS, magnetometer and air data computer, the Garmin AHRS provides an accurate digital referencing of your aircraft’s dynamic orientation in space. Also, unlike some competitive attitude/heading sensors, it’s even able to restart and properly realign itself while the aircraft is moving.