How to find Employee Engagement levels without Survey?

Dear HR Professionals,
I would like to know the ways to find employee engagement levels without Survey in Manufacturing Industry(Cement)?
Kindly Share your innovative ideas and suggestions.
With Regards,
E. Thomas Andrew,
Management Trainee - HR,
India Cements Limited.

There are employee behaviour patterns that emit employee engagement, you need to keep eyes & ears open to note, understand & interpret them.
Employee informal communication on culture, rules & regulations, perceived growth prospects are some of the indicators of extent of employee engagement.