In the videos of people plane spotting at airports, how do they hear the pilot and towers radio?

when i watch videos of plane spotting, thats when planes take off and land, the people can hear the tower and plane talking. how do they do this? heres an example. http://www.youtube.com/watch?v=gLskdLmi9Ww&feature=related you can hear it from 0:00 to 0:06