3. Improved Internet, communication networks, and first respondent services: 
Among the immediate effects of the tragedy was that people wanted to know that loved their ones were safe, but could not reach them due to the failure of communication lines. 

Even first respondent services like the fire department, NYPD and the 911 were unable to communicate among themselves, resulting in complete chaos. This has spurred several attempts to improve cellular communications and provide emergency services with the second line of communication in case of network failure. 

A major development has been the use of peer-to-peer technology to share critical information and enable people to know that their family and friends are safe.

The internet is said to have become more robust, and some steps have been taken to take care of vulnerabilities and prevent cyber warfare. 

4. Using AI to combat terrorists, detect and diffuse explosives:

Authorities now employ Artificial Intelligence systems - especially robots - to combat terrorists and get rid of explosives. This has been done to reduce the risk posed to human bomb disposal squads. MIT's I-Robot, which was created specifically for bomb demolition, is an example of this new technology.

Another major advancement has come in the form of unarmed aerial vehicles and unmanned aerial vehicles or drones which have unlimited prospects in the areas of surveillance and remotely controlling security situations. 

5. Rich data mining:

The mining of unstructured data to extract intelligence has been one of the main focus of investments since 9/11. Emails, social networking messages, VOIP calls, photo uploads, and website traffic all provide critical information about individuals and their activities.

With increased data surveillance, agencies can track down suspects at the slightest hint of suspicious behavior. This has, however, raised a raging debate about the loss of privacy. Some advocate for limiting the government's access to the personal data of internet users.