Had no commercial calls when I was a kid growing up on the ranch, didn't even know if any were available in the 40's/early 50's. So I made due, made all my own calls for all hunting. For squirrel types, tree or ground, anything that you can make a sharp bark or chirp with can work, a striker... items not intended to be "calls" and you might have laying around the house/garage. Endless possibilities to make a striker call. Kids toys as well, like the old toy clickers used at parties, Halloween, etc. Almost any mouth call can bark as well with practice, and making your own dedicated mouth squirrel calls is very easy also from household items. Calls that mimic their predators might work sometimes as well, like a hawk screech, etc. Even a squirrel tail can be used to get attention and invoke a reply sometimes to locate one, at least where snakes are a threat to them. I view them all as locator calls. However none of them always work... lots of other factors involved.
