The London bombings show a new movement of terror and anti-terror activities. Terrorists are targeting people in less protected public areas, such as subway stations, buses, etc, because it is hard for police to set expensive and big X-ray machines everywhere to detect the bombs. Thus the anti terror agents need new methods to fight with the terrorists. From what London policemen have done, it is obvious that video surveillance recordings are a big help. That is why TBUS and IPIX are having a great run now.
The other homeland related stocks that worth to look at are (1) portable detection device maker (2) identification analysis technology company (3) body protection device maker
As far as the ASEI products, they have the best technology of X-ray imaging. They are being used in White House, Congress, US border and most US ambassadors. However, they are expensive and passive.