The IR lights up, but nothing like the old flash types. Deer notice it and most will stop and look at it. Some sniff it or even chew on it. Oddly, it's just the deer that pay it any attention. Some critters that I would think would be just as tuned in to little things pay it no attention, like coyotes and bobcats.
I’ve noticed that I can hang the camera much higher than eye level and point it at a downward angle and the deer no longer notice it. This limits the effective area of the camera. If you’re looking to get a good photo of someone’s face, it would also make that harder.
The cameras I have are adjustable for duration between shots. The more shots you get as someone passes the camera, the more likely you are to get the photo you’re looking for, but you also increase the odds of someone discovering that they’re being photo’ed.
If it were me, I’d set Cam1 to get a photo of the subject of my interest. I would set Cam2 to focus on Cam1. If someone notices Cam1 and proceeds to take it, they’re probably going to get spooked pretty bad when they walk up to it and get photographed again. If they’re focused on getting Cam1, that would likely reduce the odds of them noticing Cam2.
Depending on what you’re trying to accomplish, the addition of a couple paintball grenades on tripwires may be beneficial. I know it sounds stupid, but depending on the situation and who you’re dealing with, it could help identify them. If this were a problem with the neighbors grown kids or something like that. Also keep in mind that I'm fenced and posted, so no one is going to just wonder into my area; that would make a big difference to me if I were thinking about setting up anything like what I mentioned about the paint marker.
Happy hunting!