My wife's father lives with us. Our solution was a wifi alarm, he wears the panic button and it sounds a local alarm, and also to my wife's phone, if she is out.
Amazon Alarm
Then she can talk to him through Alexa.
He can also say 'Alexa Call (wife name)' and it will call her. Or she can 'drop in' and listen in to his room.
Alexa Dialing and drop in
Reliable. Immediate contact for us, and no monthly fees, other than an Amazon account.