Most laptops that have an internal wireless antenna have some mechanism to turn on or off your wireless antenna.  External wireless adapters usually do not have a means to disable your antenna.

How to turn on/off Wireless Antenna in various Laptops

Dell - Switch on the side or press FN+F2

Hewlett-Packard - Press Antenna Button

IBM - Press FN+F5

Toshiba - Switch on the side