Yes, you need at least one Flair Puck in a Flair system. This Puck is configured as a Gateway and plugged into power using the supplied cable and adapter. The Gateway Puck is connected to your home WiFI and acts as a communication hub for all your other Flair devices (even if you only have one Puck in your system).
After the Gateway Puck, remote sensors can be used in rooms with Smart Vents to read temperature and provide occupancy data.
Note: Some homes will require more than one Gateway Puck to facilitate signal to other Flair devices. Additionally, for systems with more than 11 Flair devices, use the Large System Calculator to determine the minimum number of Gateway Pucks required.