Is there a way I can set up a direct hotline with my elderly mom between my house and her apartment that:

1) is secure
2) no one else can call
3) does not require batteries/charging
4) is immobile and can’t be lost

She has an Internet connection and a cell phone already but often forgets to charge it. Another cell or landline opens her up to 2x predatory junk aimed at seniors

I am thinking like the red Batphone in Batman ‘66