Angelina my father has 2 phones, a work phone and a private phone. it is very unlikely that both phones are broken
I think 100% security is not possible and not necessary. So it's fine if you can almost always get in contact with your father but not really always. Anything else is theoretical.
I never heard about a situation where a wearer really needed immediate release and it was not possible. Yes it's thinkable and it is good to have a save system. But it is not the end of the world if it in some rare situations can take a bit longer.