you can smell it, but as to if the deer do I dunno. I took mine with my lil girl oneday since I didnt want her first treestand hunt to be ruined by skeeters. We had 3 doe walk within 40 yards, but i was downwind though. It kept every bug away I do know
The only time I will use mine is if bugs are eating me alive. Ill put up with a few bites, but when they are about to carry me to the moon I'll use the thermacell.