I am not a fan of chihuahuas but my aunt has one. She is an insulin dependent diabetic. Too much insulin and her blood sugar goes low and she will have a seizure. That dog will wake her up in the middle of the night if her blood sugar is low. The dog has never been trained. But seems to be very good at sensing things like that. I saw a couple of people have mentioned them as well. Might be a good pick. Small enough to hold and cuddle. Small dog small appetite. seems like a smart dog without training. Good luck with the dog search.