How can I combat lunch sniffers?

Just go back to bringing your hot lunches. If others come over and ask what you're eating, just give them a look and say "My lunch." Don't add anything further, and they'll get the idea that you don't want to be bothered when you're eating.

That exact thing goes on where I work. Let's face it people love food and are always interested in what else somebody else has. I really don't think they're trying to be rude or invasive from what I've observed. I don't like it at all myself so I choose to eat in my car, even if I have to heat it up and then go out there. Doesn't seem like a concession you should have to make but I don't think it's worth being defensive about and creating hard feelings. They aren't going to change, and they'll just alienate you if you are defensive.

OMG! I know exactly how you feel. I HATE nosiness when it comes to what I'm eating for lunch and have decided to eat at my desk because people seem to be less nosey when I sit there than when I sit in the lunch room. People have come to me to see what I'm eating. Usually an "eye roll" keeps them away or I will use the container or the bag that it came in to cover it. It worked for me.

Good luck!

Just keep bringing the hot lunches!

When someone comes and asks what you have, tell them once and then go back to eating. If they stay there, look up at them and ask if they would like to say something. If it still annoys you, tell them so! Say that you feel uncomfortable with them standing over you and if they could please go back to their desk.

Or, you can keep a small bowl of candy ((like mints or individualized wrapped Starbursts to bribe them away.

You seem to be a strangely anti social person. Can you honestly say if you saw your friend eating something that smells good, you really would not ask what she is eating? It is totally normal in workplaces all over the world. Perhaps you should quit your job and start up a home business