So you will be using the Miles Tag protocol. To detect this you will probably need a micro controller of some sort.
Suggestions:
- First, try to prototype your solution with a standard Arduino
- Once you have the prototype working, you will be in a better position to judge the next step.
- you will know how many pins you require, how much flash & how much RAM.
- after that you will know which ATTiny model or alternative will work (if any)
If you don't actually have to fully decode the Miles tag protocol, you could also devise a clever scheme just to detect a valid miles tag signal.
I don't recall seeing an Arduino library for decoding Miles Tag, but there may be examples on the Miles Tag forum.