We don't have a diabetes alert dog but I can tell you that our dog definitely sensed Erin's high blood sugar before she was dx. Erin had just come home from school and had just finished her snack when she went upstairs to her room to do her homework. Our dog kept getting "in her face" and climbing all over her lap to smell her---something she had never done before to her or her sister. We laughed it off at the time that "Annie" was loosing it, but now in retrospect I know she smelled Erin's ridiculously high blood sugar. Erin was dx a day or two later. I truly believe that dogs could be trained for this!