The Thermacell Patio Shield Mosquito Repeller is a compact and stylish device that looks great on any patio or deck. Thermacell Patio Shield is powered by a Thermacell fuel cartridge which creates heat to activate the repellent Allethrin, a synthetic version of a naturally occurring repellent found in chrysanthemum flowers. Heat disperses the repellent creating a 4.5 meter zone of protection. Thermacell products are safe, effective, and come with a 100% satisfaction guarantee