All data from the FAA is delayed by at least five minutes unless you can show an actual need for real-time data. Additional information is provided in their agreement for accessing the data (below).
As others have pointed out, there is various hardware that can be used to see real-time data in a small local area, but it only shows aircraft that are properly equipped.
As far as going into a control tower, take a look at What is the security policy for getting into a Control Tower?
From the FAA ASDI Memorandum of Agreement:
As a result of the aviation-related attacks of September 11, 2001 in
the United States, the FAA reviewed security risks related to the
ASDI/NASSI feed and determined that only Subscribers that are Class
One Users are authorized to receive the full near real time ASDI and
NASSI data set (this includes Direct Subscribers with Class One
Indirect Subscribers). Subscribers that are Class Two Users are not
authorized to receive near real time flight tracking and position
messages. Class Two Users are only authorized to receive the full
ASDI and NASSI data set that has been time-delayed at least 5 minutes.
Class 1:
A Class One User is a professional aviation organization with an
established flight dispatch or planning function that requires near
real time positional flight-tracking capabilities. This organization
must have direct responsibility for dispatching or tracking aircraft
it owns or be contracted by the owner of the aircraft to do so.
Examples are airlines, regional air carriers, air taxis, any
organization providing dispatch or tracking functions for aircraft
owners, flight operation centers, government users (as described in
Section
5.5), and professional flight planning service providers. Fixed Base Operators (FBOs), corporate flight departments, and part 135 operators
must have direct responsibility for dispatching or tracking aircraft
to qualify as a Class One User. The FAA shall be the final arbiter
for any disputes regarding the interpretation of this Section.
Class 2:
A Class Two User is any user not meeting the criteria of a Class One User (e.g., most general aviation; non-aviation-related
entities and individuals; any other entity without a specific
requirement for near real time positional flight-tracking). Class Two
Users can obtain Class Two (time-delayed data) either directly from
the FAA Traffic Flow Management System Hubsite Class Two ASDI/NASSI
interface or from Direct Subscribers that provide time-delayed Class
Two data.
