On Wednesday, January 13, 2016 at 6:21:40 PM UTC-5, wrote:
Well that got technical right away. In general terms, would I be able to know about small aircraft with transponders, ie C172 etc, flying into the airport I fly? It's a class E airport, but near a class B airport so, most aircraft are transponder equipped. The device I am looking at is an ADS B - in, receiver, and I would send the information to my iPhone 6+ via wifi. It seems like most major areas now have ADS -B coverage and since I don't have to install an ADS-B out signal, yet. It seems like a solution to what I am looking for, which is some indication of another aircraft near me when my eyes did not pick him up.
Since I am not sending the "out" signal, would I not receive the transponder only traffic? Also since the "out" signal is not present, would the set up just report useless information to me and maybe even show my own glider as traffic?
The device I'm looking at is a TRX1000 from Air Avionics, used with iGlide software.
Thank you.

While you may see Transponder equipped aircraft transmitted via TIS-B by your local ADS-B ground station, this only happens if there is and ADS-B OUT equipped aircraft in the area. The ONLY way you can reliably expect to see all Transponder equipped aircraft in your vicinity is if your own aircraft is ADS-B OUT equipped.

Personally, I think that installing an ADS-B IN receiver without an ADS-B OUT transmitter is a really bad idea. It will have a tendency to make you falsely think that you are seeing all the traffic out there, which will inevitably breed a very dangerous form of complacency.