Thanks guys!! That what it is, the seat belt tensioner.

Thank you!! I'll take a picture tomorrow and post it.

Hello, I am new here and have a 2002 S60. I noticed that there's a part mounted in between the rear deck panels in the trunk, It's in the middle and is a hollow cylinder with two wires going to it. It looks like some type of sensor. Any idea what this is. I've searched and haven't found anything abo...