Place TWO Buttons at the most Visible and Accessible spot in the office. With a signage: One is labeled Happy and the other one is labeled Sad. It could be extended as 1, 2, and long for different level of feelings.
This will be integrated with Qualtrics for Question Less survey.
See Max's "Qualtrics for Instant Survey" post at:
https://medium.com/@maxtsai/qualtics-for-immediate-feedback-fe922c67e24c#.oo5d53x6t