GREAT DEAL!!! Lumen analyzes the %CO₂ in your breath and determines if you are using mostly fat or carbs for fuel based on the CO₂ concentration. Lumen has been validated to match the gold standard for metabolic measurement with an at-home, handheld device. LUMEN health metabolism tracker. Bought brand new from the LUMEN website online and paid full price. Don't pass this one up. I take great care of all my items! From a very, clean smoke and pet free home. Don't succumb to retail pricing ; )