My mom has Alzheimer's and is seeing people that aren't there. How do I explain to her that nobody is in the house?

No, you don't explain that they are not there. Moms Neurologist explain to Mom she may see things but not to let that bother her. He told me if her "seeing people" didn't upset her than don't worry about it. Mom saw a little girl. She must have been a pistol because I could hear Mom saying not to do this and that. As soon as I showed up the little girl disappeared.

The only thing he told me I should worry about was night terrors. That if Mom had them more than 2x a week, he would prescribe something. When she seemed to be having one I would wake her up and tell her to open her eyes. Then I'd tell her to go back to sleep. She would be OK the rest of the night.

Play along. Check the house, her area. Then tell her if someone was there they are now gone. If these people frighten her then maybe the Dr. can prescribe something.

My husband sometimes sees wispy trails of colors....which I think is kind've cool. I ask if they're moving, what colors, and how big they are. If he starts seeing other things, will do the same. I just roll with it. Reminds me of children who describe all kinds of imaginary things in their lives.

Is she taking Ambien?  It can cause hallucinations.

Is your Mom on an Meds? Regardless of if she is or isn't you may wish to discuss her hallucinations with her PCP or nuerologist.

Depending on her stage of Alzheimer's, "explaining" something to her and getting her to understand it and therefore change her behavior may be impossible. It may be impossible to remember that fact that you've explained it less than 10 minutes ago. The Alzheimer's brain doesn't work the way it used and it has a very different reality than the non Alzheimer's brain. Recognizing that may help you cope a little better.
Good Luck

Hello
Been there! I have found that the word " explain" is something difficult. "Explaining", under other circumstances, leads to understanding. Not the case anymore.
I've found that I treat this situation as one would if a youngster has had a bad dream- comfort, console, and don't dwell.
Piece of chocolate always helps!