Fly trap

We have had lots of flies hanging out in our house. I think it is from the beautiful weather and opened doors, but they just pester us. I have tried the fly swatter, but all the smart ones must be left now. Occasionally one will fly to an open window, but get stuck because there is a screen. When they do this I like to close the window and trap the fly. Not sure I should admit this, but the kids think it is great fun too. What do you for cheap entertainment?