A tool? Not sure, but I find this fun and super effective. It is a small horn you blow on and any crow in the vicinity comes toward you immediately. We are bird enthusiasts. My 16-year-old son has attracted several hundred crows within minutes with this. It is pretty fun. Visitors to our house love to walk outside and start tooting on it and then crack up when the inevitable crows wheel overhead.
-- Alex Giedt
Acme 4873 Crow Call
Available from Amazon