I have a really good and simple idea but I don’t use social media and even if I joined today I wouldn’t have many followers:
Just a simple sign taped to the front door that can be printed out every week or two that is a calendar (maybe with just the current and previous week, not the entire month) that reads something like, “If I’m okay, I’ll mark yesterday”. People can draw out a calendar if they don’t have a printer or they can print out a pdf. The web address would be simple and easy to remember and on every sign. Encourage people to do so clearly and as big as possible. Just mark the previous day every morning (pref) when you wake up. This way, anyone walking by can take notice and knock (or kick) if two days haven’t been marked with an “X”. People can communicate through doors and not open them. Instructions would be clear and specific. A single, uniform way.
I know this wouldn’t be as beneficial to people that are in rural areas that may not have neighbors. Unless, police patrolled. But, that would take a lot to get going. Who knows. A lot of people are dying at home and I worry about their dependents and animals, as well.
Everyone stay safe.