title: Unique machine ID for arduino project
body: <p>I am building some remote sensor nodes for arduino, they will use RF to transmit data back to a base station.  Is there some sort of unique id backed into arduino that I can use to identify the remote arduino sensor node to the base station?  If not, how do others solve this issue?  </p>
  
  <p>I realize that I could hard code a nodeid when I compile the source for that node, just seems like that would not scale too well.  What I need is something analogous to a mac address in http land.</p>