Brand new, still in the box it was shipped in. I bought it the last day of class and have never used it. Apparently, CO tests during home inspections are not common here; my field instructor had never even seen one. So if you're itching to try a new gadget, or if CO tests are common practice during inspections in your area, by all means, buy mine! I bought it for $505, and I'll gladly give it to a new home for $465 + shipping. Tool Experts was going to charge me a 20% restocking fee, so I thought I'd have better luck reselling it on my own. Purchased April 2010.