I can always tell with Alphy because there will be a couple yellow dots. Most times he pees in them though when I'm gone to work. I try not to keep one when I am home because I worry about infection, but I will put one on him if I get busy around the house and it's been a little while since we've been out. I picked up a trick from some YT'ers
and bought baby wipes and wipe him off with one every time I take it off and sometimes when we come in from our walk if he's stinky.