At a legitimate inspection station the first thing they do is a visual inspection for mods like missing or gutted CATs and disconnected or disabled emissions devices. Check with the bandits in your area to find the inspection stations that accept bribes to overlook this stuff.
Removing the CATs is a federal crime that is seldom enforced but I'd probably be the guy they'd set as an example.
I've been to three different inspections stations in Washington over the last 4 years, never once had anyone look under the car or anywhere around the car really. They're just a bunch of underpaid government employee's who don't really care around here luckily.
After thinking about it last night, I remember that they do plug into your cigar lighter if you have a pre ODB car, it's their way of testing voltage. They then stick a smeller tube up your tail pipe and do a dyno run (had a 91 geo metro daily last year that required this). For ODB cars however all you do is pull up, they verify VIN then plug into computer and you're done! Just went through the station on Aurora in Seattle last week in my girlfriends Toyota.
By the way our cars require 2 HP Tuner credits so $100 ($50 per credit) will unlock your car and we can do all the changes you want like CEL lights, CAGS, Fans Temps, Speed Limiters, etc, etc.