I don' t know if deer are alerted by squirrels. I would say in some instances yes, but most of the time I don' t think it alerts them. On the other hand I have been alerted by squirrels of deer movement though. I always pay attention to squirrel behavior when I' m in my stand. On more than one occasion I' ve had a squirrel go nuts and a few moments later I' ll spot a deer. If you hear a squirrel start barking and going crazy, get ready, sometimes that comotion means a deer has that squirrel riled up.