Can you identify this please?

[grumpyoldgit]

W203 C270

Didn't know whether to post this in Interior or Electronics, so as it's connected to the electrics went for the second option.
I removed the rear seat cushion and access panel to lubricate the parking brake linkages and this item is beneath the seat cushion. Haven't a clue what it is or it's purpose. Anyone know?

 

[Troon]

Seat belt pretensioner? Schloßstraffer is a "firm-closer".

 

[misfire84]

and it is explosive !!

 

[BlackC55]

Its a belt buckle pre-tensioner

 

[grumpyoldgit]

Many thanks guys, appreciated