Our Dry-Packs brand Cobalt Free Humidity Indicator Cards are safe to use and do not contain Cobalt Chloride. These cards have three indicating dots that start with a light brown color (dry) and changes to a pale green color (humid) when certain levels of moisture are present. Humidity indicator cards provide external monitoring of humidity levels inside closed containers and packages with three stages. The first stage starts with thirty percent, which warns you moisture is becoming apparent. Next, forty percent indicates that it s time to replace the desiccant at this stage. The final stage is fifty percent, which indicates there is enough moisture that requires examining the item to determine if replacing the desiccant is necessary. They pair well with our Dry-Packs brand Silica Gel Packets and help prevent moisture issues that can damage items like electronics and guns. To use, simply place a humidity indicator card and a desiccant (such as silica gel packets) with your items. Over time, you ll be able to quickly glance to see if your item is safe from moisture. These cards meet the requirements of Military Specifications: MIL-1-8335 and MIL-P-116 Method II. Each card is two inches by three inches in size. Includes 50 Cards.