Currently the only official firtst party input device for Daydream is the Daydream controller. Google Cardboard applications can use a variety of third party controllers to take input.
The Daydream controller allows 3 degrees of freedom, providing rotational and positional information, a dual axis touch/click controller along with 2 extra buttons.
For information on how to take input from this device see the Google Daydream Controller documentation.
2018–03–27 Page published
Google VR documentation updated for Unity XR API in 2017.3