The Nitecore EMR30 is a powerful dual function mosquito repeller that creates a comfort zone free of pests in up to a 20ft radius with the EMR30 for family picnics, barbecues, and holidays. The EMR30 accepts up to two blue pyrethroid based pads that are activated by electronic heating. This means no more messy or expensive refills and no fire hazards. You can double the pest repelling potency by also activating the 25k-40k ultrasound function to drive away annoying bugs.