I also use my voice. Lots of barred owls around here and they usually call for me very early in the morning. If they dont and it is about to get light and no birds have gobbled yet, I rip out a loud whooo Just one long note with the gutteral sound at the end. This is the sound that the owls make sometimes and it usually gets a shock gobble. If that doesn' t work I wait about 2 minutes and yell out a who cooks for you who cooks for you all. I have tried cannister owl hooters and they weren' t loud enough.