ThermaCELL Patio Shield creates a 15-foot zone of mosquito repellency, ideal for decks, patios, and other outdoor areas. It uses repellent mats and butane cartridges to generate a repellent vapor that keeps mosquitoes away. The device is easy to use, simply insert a mat and cartridge, turn it on, and enjoy your outdoor space. The repellent is effective for up to 4 hours and the butane cartridge lasts up to 12 hours. ThermaCELL Patio Shield is a safe and effective way to keep mosquitoes away from your outdoor gatherings.