Am I Breaking The Law By Having This In My Home?

My fiancé and I are getting ready to move out of our apartment soon, so my current landlord is showing it to prospective tenants. All of our stuff is still in there, and honestly I'm a bit uneasy with the idea of strangers coming into our home without us being there. Will they touch anything? Or even worse… will they take anything? I know I'm probably being a little paranoid, but I just don't like it. However, I understand that my landlord wants to have someone lined up to move in as soon as we're out, so that's just the way it is.

Yesterday, as our apartment was being shown, I remembered that we have a security camera set up, and we can watch it any time on our phones. But when I went to take a look, my fiancé said "Wait, you can't do that… it's illegal!" Hold on… why the heck would that be illegal?? She said that you can't film anyone without their permission or knowledge. But is it really against the law? We talked about it on the air this morning, and asked if any lawyers or anyone familiar with the law could let us know. We got the following message from a listener:

per your question about recording in the apartment - you simply need to post a sign "property under surveillance" or "video surveillance equipment in use" - something to this effect.

But here's the thing - do I really want to hang a sign like that in my home? I did a little searching around on Google for more opinions, and several articles I read said that it's okay, as long as it's not in a room like the bathroom or bedroom. There's also the fact that the law in Maine could be completely different than anywhere else. So pretty much… I'm even more uncertain about it than before I started trying to find out if it's illegal or not. So for now, I'll be putting the security cam away while our place is being shown. I'll just have to really keep my fingers crossed that no one touches anything.