While the US scrambles to get new security structures installed, contractors and airlines are already studying the next generation. The general idea is to use "biometrics", in which something (a fingerprint, retinal pattern, or DNA) provides positive identification and a database establishes if a given person is extremely unlikely to be a threat, or if they are on a "watch list" by security agencies. Some are concerned that with such databases, the airlines might use them to target customers with advertising keyed to their travel patterns.--Stephen V Cole