There are six basic technology type "solutions" for aircraft security.
1.Cockpit separate from cabin. Either through entirely separate access or through strengthened bulkhead/door of current practice
2. Surveillance/communications: various combinations of cameras, peepholes, radios, microphones, panic buttons and other communications technologies to provide intra aircraft or air to ground surveillance of cabin and cockpit.
3. Countermeasures in aircraft: various countermeasures , both active and passive, covering the range of lethality and obtrusiveness. Various weapons, gasses and other drugs, aircraft pressurization and law enforcement personnel. Design features that limit pax mobility and ability to interact with aircraft or crew. various aircraft hardening concepts.
4. aircraft as countermeasures: variations on aircraft being remotely controlled, on a programmed flight path, limited control or navigation authority to deviate from planned route of flight. Unresetable transponders, beacons, automatic signals, PINs, deadman switches, simulated turbulance induced by flight controls and fun house floors. Various kinds of data linking of extensive aircraft state and internal surveillance information.
5. preflight: preflight security of aircraft, crew and passengers
6. airport and airport environment