Caregiver pager that will work next door

My elderly father is trying to stay at home, basically alone. We do have a lot of family nearby, including my sister in the house next door. We need a simple “panic button” that he could push to let someone at the house next door that he needs assistance.

We don’t want him trying to use the phone and don’t want to subscribe to one of those medic alert services that alerts a central dispatch desk. We don't need motion sensing or fall detection or anything like that.

We have tried one of those cheap RF “caregiver pagers” that you can get on Amazon for thirty bucks. They have a little sender he can carry around his neck or whatever and receivers that either work off batteries or plug into the wall. The one we tried works off batteries. It serves our purposes perfectly, except it doesn't work reliably in the house next door, presumably because they are brick houses?

Do any of you know if there is a simple pager like device that will work reliably in the house next door? Walkie Tallkies can do it, so it seems like there should be something simple.

Thanks!