Force Touch sensor? Still working after a screen replacement.

Force Touch sensor? Still working after a screen replacement.

I changed the screen to my A1554 Apple Watch. When taking the shattered screen off, I didn't realize there was some kind of a sensor so I tore it off. I replaced the screen with a new one and assembled the watch since I didn't have the a new sensor. Now, however, force touch is still working just fine. What's the purpose of that adhesive ring? Do I need to get one?