Fox Pro has a Squirrel Distress sound. I think it's meant more to call predators than squirrels. I have it on my FX3 and have used it successfully to call fox, bobcat, and coyote. I also have used a Faulk's Squirrel Distress hand call to call coyotes. I view it primarily as a prey distress sound to call predators with. I've seen coyotes stalk squirrels in the woods and scraped plenty of little squirrel claws out of their scat when trying to determine what the coyote has been preying on. The same can be said for the bobcats and grey foxes that inhabit the Ozark timber. There are usually a lot of squirrels in the timber here and they play a part in the food cycle of all the predators. BTW, that includes Redtail Hawks and Owls. I've seen those two birds of prey take squirrels also.
The FX3 Squirrel Distress has sparked some reaction from the squirrels themselves. The very first time I used it a big fox squirrel ran through the tree tops chattering and sat right over the top of the caller looking hard at the Predator Supreme decoy as if it were eating a baby squirrel of ol' Mama's there. Most often the nearby squirrels run out on a limb and do one of two things. They either bark and chatter at the sound and then slip off. Or, they freeze and sit silently watching the caller/decoy. In the latter case they are very, very, still and motionless.