To test if you have the factory alarm that's standard on the Limited, roll down a window, lock all the doors (either by the remote or through the master switch on the door), wait about 30 seconds, reach in, unlock and open the door. The horn should honk and lights will flash (same effect as pressing the 'panic' button) if you have the factory alarm.
Good aftermarket alarms would be Viper or Clifford (now owned by DEI).