Seatbelt
 

Does the third gen fit have sensors to apply the seatbelt lock when braking while going downhill? I noticed while braking to make a turn on a downward hill, my seatbelt was tighter than usual. I wasnt braking too hard, so im curious if these "sensors" exist?

I believe that is what's called the pre-tensioner: What is a Seatbelt Pretensioner | Autobytel.com

Contrary to 2Rismo2's link, I've only heard "pretensioner" applied to the third (pyrotechnic) class they mention (though some modern ones are electric rather than pyrotechnic, and may be used multiple times and so triggered by non-accident conditions). The other two are just locking the seatbelt so that it actually does something, not tightening it. Wikipedia agrees with this distinction, for whatever that's worth.

Every modern car has some sort of a seatbelt lock mechanism, generally triggered by forces in a horizontal plane (so braking, turning, or hard acceleration). It's possible that the combination of braking and turning added together were sufficient to cause it to lock. It may be that your Fit also has electric pretensioners that activate under relatively high G situations; that I don't know for sure.

The Fit has one-time-use explosive pretensioners controlled by the SRS unit. What you're experiencing is a small weight built into the retractor that locks at about the point your body would start leaning forward. Mine locks frequently when going downhill, and it's annoying, but just part of the design.