TPMS air sensors for G8 wheels
 

When you get an aftermarket set of wheels, you need to either transfer your originals over to the new wheels or you need to buy new ones. Originals are about $80/ea from GM. Even aftermarket ones seem to cost $25-$50 each. This auction has a full set for $50! I have successfully installed and tested them. Unless they have junk batteries, these are a winner.

http://www.ebay.com/itm/4-NEW-GENUIN...item43b2f38cdc