1-hour phone interview with engineering hiring manager. Brought me in for a 3-hour presentation covering one of my own projects. Then a coding challenge in C, not very difficult. Then 1-hour phone interview with a firmware guy. Then a 4-hour interview with many people in the engineering department. The vibe at Fitbit is very positive and high energy. Lots of people between 25-35 and the bright sunny office is in a choice location in downtown SF.