Your second idea has already been done, to a certain degree. http://www.hindawi.com/journals/wcn/2005/930810/abs/ http://www.hindawi.com/journals/wcn/2005/93081

Your second idea has already been done, to a certain degree. http://www.hindawi.com/journals/wcn/2005/930810/abs/ http://www.hindawi.com/journals/wcn/2005/930810/abs/ is one example of a (highly miniaturised) sensor network that communicates with a corner-cube retroreflector returning modulated laser light back to the base-station. It has no active comms emission.