Sharing this for others who has the same issue with the similar 3-way switch configuration.

I had an issue with 3-way lights on my house. One side of the 3-way switch box has neutral wire, but the common terminal of the switch is wired to the light (meaning it is switched and not always hot). The other switch box does not have neutral, but the common terminal of 3-way switch was hot (line).

HS210 needs to be installed on the line side so that it gets power constantly even when the light is off. 

This is what my 3-way configuration looked like before, and how I revered the line and the load so that I can install HS210.

I hope this to be useful for someone. 

Note that C stands for Common, T stands for Travelers. I didn't draw ground wire for simplicity.

Warning: There are many different 3-way configurations and this does not work on all cases. Don't blindly apply this. Make sure you verify your configuration.