If you're an American abroad, the NSA could find out where you are right now, if they wanted to. According to documents leaked by Edward Snowden, the agency's collecting 5 billion records a day on cell phone locations around the world. Some of those are from "incidentally" domestic cell phones.
According to a report by the New York Times, the NSA tested a system to collect location data from American cellphones in bulk back in 2010 and 2011, before ultimately tabling any plans to roll it out. For now, anyway.