There were several different restrictions on civil liberties since 9/11. This includes:
1) Passing of the Patriot Act- This law gives the government more freedom/flexibility to use listening devices and wiretapping strategies in order to catch individuals who may be planning an attack on American soil.
2) TSA- The creation of the TSA ( Transportation Security Administration) completely changed the way Americans fly. This federal agency has individuals go through a thorough check before entering the airport. This can include a metal detector test, putting their bags through an X-ray machine, etc.