ood Knight Advanced Activ+ Cartridge Twin Saver Pack contains mosquito repellent cartridges that are designed to fit into Good Knight mosquito repellent machines.The cartridges are designed to provide long-lasting protection against mosquitoes, ensuring a comfortable and mosquito-free environment.To use, simply insert the cartridge into a compatible Good Knight mosquito repellent machine, plug it in, and turn it on to release the mosquito repellent vapors.