Try using it outside. My finder doesn't work indoors as it picks up on the TV, the dehumidifier, the halogen heater, my ipod docking station, etc.
What is all this business about the batteries being put in opposite ways? That's utter bullsh!t, I have a working collar in my pocket right now and the batteries go in negative side first and IN SERIES. You never put batteries together with + and + or the negative terminals touching.