Radon testing kits are designed to measure the concentration of radon gas in indoor environments. These kits typically include a device that can absorb radon or detect its radioactive decay. There are two main types of radon testing kits: short-term and long-term. Short-term kits measure radon levels over a period of 2 to 90 days, while long-term kits measure levels over a period of 90 days to one year.