My father is taking care of my mother who has Alzheimer's...

My father is taking care of my mother who has Alzheimer's and I'm worried that something may happen to him healthwise and no one would be notified. He has high blood pressure. My mom would not know something is wrong and would not call the paramedics. How do you handle this? I'm thinking some kind of medical alert system. Also, I know about the jewelry for a wandering dementia person, but what do you do about her leaving the house and my dad not knowing. He wears a hearing aid and does not always hear well. Any advice?