In PA it depends on what County you live in. Some counties are more intrusive then others. In high population counties they sniff the exhaust. Others they only check the gas cap, and I think there are still some that don't do anything. If you drive less than 5,000 miles a year you don't have to have your exhaust sniffed no matter what county you are in. Cars with a classic license plate (15+ years old) don't require the exhaust sniffed Cars with the antique license plate (25+ years old) don't require inspection at all.