An event spray/party spray is for parties and events when there are 10 or more people in the yard at one time. The reason for this is our product works in two ways: first, the spray will eliminate mosquitoes and other small insects on contact. Second, the spray repels mosquitoes. Our product has a scent added to the spray (we don't smell it, but mosquitoes do) that repels mosquitoes and keeps them out of your yard. So instead of smelling humans, mosquitoes smell the scent and stay away. The repellent scent lasts for 21 days. The reason we suggest a double spray for parties and events is because when there are more than 10 guests in the yard, the scent of multiple people tends to over power the scent of the spray, rendering it less effective. By treating with a double spray we put a double application down, hence making the scent stronger, and therefore providing adequate protection for you and your guests.