Don’t expect your Apple Watch to be on you every time you go through the airport — especially when you’re going through security. It’s a good idea to remove it along with everything else you want to put in one of the small plastic bins before trying to go through the metal or body scanners, depending on the airport.
If you’re worried about someone stealing your watch, don’t be – TSA agents are keeping an eye on the X-ray transmission belt, so it’s impossible for anyone to walk by and touch it. But you can always put your valuables (Apple Watch, iPhone, wallet, etc.) under the basket and put a jacket, sweatshirt, etc., on top of them to make it difficult for anyone to do it. look at the X-ray to see if they are in there.
Alternatively, you can quickly remove your Apple Watch and put it in your bag before going to security. That way, it will be placed inside your closed luggage (which will still go through the X-ray machine) without going inside one of those open bins.