I'm not encouraging anyone to go out and get a dog but I can try to answer your questions. I don't know the distance that a dog CAN alert. I do know that dogs can "smell" underwater, in vats of gasoline, and in dense smoke. Dogs can smell more than one scent at a time. There's isn't any reason that they can?t smell their person out of hundreds of other people. Heck, a family pet can even do that without any training. I have a friend in California whose dog alerts while he is playing football. I have a friend in West Virginia whose dog alerts from in the house while the diabetic is riding her bike in the front. Freaky but true! My dd's dog has and does alert her while she's swimming in an Olympic size pool and the dog is on the other side. He alerts her in our smaller pool. He alerts her while she's at track and cross country practice and across the football field while he is on the side lines and she is on the field. I guess the most impressive alert was when my dd knocked 2 of her front teeth out & was in the dentist office getting them repaired. I was in a wheelchair and the room was tiny so she left her dog out in the waiting room with my husband. We were in about 3 rooms down a hall and through a closed door from the waiting room. My husband texted me & told me to have my dd check her bg. I asked why? He said that her dog had been sound asleep under his chair. He suddenly jumped up, lunged at the door to the hallway we were down and alerted to a low, and would not quit staring and whining at the door. Sure enough, my dd's bg was low and the dentist had to stop so she could treat. The dog ONLY alerts when there is a high or low. The dog doesn't alert any other time. You can train them to do a "non-alert" which is when you ask them to "check" you and your bg is fine so they give a "non-alert". My dd's dog doesn't have a specifically trained "non-alert". If she asks him to check her and he checks her and does nothing to indicate low or high then she knows she is in range. Was that your question? Some dogs are more accurate than others. A dog can be 100% accurate. I know this for a fact because we have one. My dd's dog gives a "high five" or uses his paw to touch her pump, leg, foot, arm to indicate a low. He nudges with his nose on her pump, leg, arm to indicate a high. If she ignores him then he will go to another person and alert the same way to "tell on her". Our trainer and I, personally, have both looked into your next question. I think it is mainly based on smell because the "air-scenting" dogs seem to be most natural at this and can alert from distances. However, I also think that body language and interstitial fluid changes have much to do with it as well. Our dog that alerts at 100% will not only "check" your breath but will almost always verify with a check to your eye (interstitial fluid), as well. I've seen other alert dogs do this at times, too, so there is something going on they are picking up from the body fluids. No, not a stupid question, but NO , dogs shouldn't ride rollercoasters. I can?t imagine that they would enjoy it at all. When my dd goes to an amusement park, she waits in line and when it is her turn to ride she passes the dog through the ride to the "getting off" side of the roller coaster where the dog will wait until she gets off the ride. Much the same as passing your camera, hat, or other items over to wait for you to pick up when the ride is over. Her dog does enjoying riding the "car rides" though, and service dogs are allowed on several rides at Disney. Her dog also enjoys riding in the boat on the lake and riding on the tube behind the boat. Not many dogs will nor should get on an escalator but her dog doesn?t even hesitate. I can't say a certain breed is better than others. It has a lot to do with the structure & size of the nose (a small, squished pug nose would not be best). Beagles, of course are excellent, but they are ground scenters. It has most of all to do with temperament and willingness to serve. Just because a dog CAN do this type of work doesn?t mean he WILL do it or will love to do it. We have a perfectly capable Golden Retriever with excellent manners and public access who CAN alert but she doesn't want to. She just wants to be admired for her beauty. You have to have a dog willing to save your life. Not all dogs will. My daughter's dog is a black lab mix (mixed with something with enormous feet!). I hope I answered all your questions. If not, please let me know and I will make another attempt, hopefully not so long!