In Colorado it depends on the county. Some are no emissions, some are just E checks and others sniff test. Lucky me I live in the strictest county. But I will tell you this, around here you don't dare take your car into an exhaust shop and ask to get your cat taken out. They will laugh you right out the door for it. You just gotta be careful depending on where you live. I ran catless for 2 years until I had to do my most recent emissions test. Now I just have a magnaflow welded in.