I bought one last season after hearing how neccesary they are to keep the mosquitos away during early season. The Olive unit is roughly $22 and the realtree hardwoods unit is $30 and each refill last up to 12 hours and cost $6. It's powered by a butane cartridge, this convenient unit creates an invisible, odorless protection by heating a chemically treated repellent mat. Covers up to a 15' diameter area.