Oxygen sensors and absorbent are some of the very few items on our website that are NOT returnable, because we can't know with absolute certainty how they were handled once delivered. Additional shipping and handling of the return can also degrade performance. These consumables are critical to safety in diving, and our customers have a reasonable expectation of receiving as factory fresh a product as possible from Dive Gear Express. Your complete satisfaction is our goal, so please consider carefully before purchase.