Perhaps stupid question. Once you have created an automation with NFC tags, are they activated only by the phone that created them or also by other phones with HA installed?
And how are tags created outside of HA handled? From all phones with NFC enabled or just the one who wrote it?
You can use the NFC tags with all phones that have the home assistant app installed. On all other phones, a home-assistant.io website will be opened.
The link will look something like this (just the identifier is different for each tag).
What happens behind the scene is that when you create an NFC tag, a specific url will be written onto that NFC tag. If you scan that tag with a phone that has the home assistant app installed, this url will be opened by the home-assistant app (so that the given action will be executed - please note that the tag only contains a given identifier so it does not contain any confidential information - e.g. if you want to place the tag somewheres public that won’t be a problem). If you scan the tag on a phone that doesn’t have the home assistant app installed the browser will be opened but nothing will happen (just as if you open the example link I posted in your browser).