I bought an insulated medical thermos, with a gel pack inside, and a sensor on top that when you touch it, it would show the inside temperature. It was great. At every TSA I would take it out and put it in the bin, and tell the TSA as I did so that it was a medical thermos. It went fine until Frankfurt. After I crossed through the scanner, I noticed all the other passengers clearing away rapidly. I thought, "Wow, someone has something bad, and I better grab my bag and clear out too." I could see my bag set aside in a separate area. Suddenly I was surrounded by heavily armored guards with their hands on their handguns. A fifth one walked up right in front of me, with his hand on his machine gun. They questioned me for about 5 minutes but would not accept my explanation. They wouldn't touch the thermos, but wouldn't let me show it to them either. It was terrifying, since the whole time their hands were on their guns! Finally one got brave and opened it, and let me go. Moral of the story: from now on, lay the thermos out OPENED in the bin! I'm laughing in hindsight.