Kills flies indoors with a fly swatter, flypaper, or a homemade apple cider vinegar or wine trap. Fly swatters are a common way to kill houseflies, and the device is also available in electric models that zap the fly instead of crushing it.
Fly paper is a sticky paper that is hung from the ceiling or placed in the corners of windows. The adhesive on the paper traps the flies. Apple cider vinegar or wine in a glass can attract and drown flies. Pour some of the vinegar or wine in a glass bottle or jar, and top it with a funnel. Add a drop of dish soap to the liquid to reduce the surface tension. The flies fly in for the food and are unable to find their way out or drown in the liquid when they try to step on it.