That's the one that detects all your WiFi data and sends it to the Chinese
Seriously though, I'd assume you have a manual that will detail what / where it goes?
From a quick google, to me it looks like a thermostat with a 60 degree C cut-out.
KEY BENEFITS Clubs-shape contact,jointing better with spot welding Miniature size Positive make and break with snap-action disc Re... Ships from China.
www.ecplaza.net
My JBD (the overkill one) didn't have that sort of sensor - I just got 3 regular temp sensors.