I'd seen only one of the links you provided before. They're interesting but, from what I've seen so far, just miss the mark, as do many others.

The LPRA one, for example, has links to makers of the right sort of products, but not both small and simple enough, as it would be necessary to use a product made for some other function, normally one with human interaction, hence large box, battery, buttons, etc. and I want something really small. The biggest thing will probably be the coaxial low-voltage power connector. I've considered using multiple car-key-fob transmitters, as each one represents a unique id and has several functions. Those certainly don't cost much. I'm not aware of a both cheap and small receiver for them though.

I just want to send a message saying ID#aaaaaaa,mmmm where the id number,a, is in the range 0..127 and the message,m, is a 4-bit value. The local MCU will also want to receive a message such as ID#aaaaaaa,kkkk, where the id number is in the range 128..255, and k is a 4-bit value. It could even be simpler. I don't want to limit anything because I don't yet know what's "out there."

I'll have to explore these links further, perhaps contacting some of the represented vendors with the "right" questions.

RE