Infrared is used to detect large grow houses or large outdoor fields. Large grow houses give a lot of heat from the lights, and large grow fields show up at a certain frequency because cannabis has a very unique heat signature... a very hot one, actually.

If your growing less then 10 I wouldn't worry about it. Just try to blend your plants in with the natural environment and you should be fine unless a hunter stumbles up on them or something like that. Don't worry about.

I worry too much, to be honest. I actually bought a motion sensitive camera (the kind that game hunters use) to give me peace of mind. I have it on a tree overlooking my grow. If anything steps in the area it snaps a shot of them and keeps it on a memory card, day or night (infrared flash for no visibility). I have a lock on it so no one can mess with it and erase the evidence. I get pics of deer and rabbits all the time. If I ever see a person in my grow spot... then I know not to ever go back.

Plus I can always check the memory card before I do work on my plants, so the worst evidence against me if someone is staking the plants out is that I had a camera in the area. Like I said though, I worry to much. Cops (in my state at least) just trash your plants if they find them...