Civilian security requirements have gone up in recent years with increasingly, the need for protection of venues from Federal buildings to sports or music hall.
One of the main requirements here is to prevent excessive queues to enter the venues but still locating possible threat. As an added complication, everyone nowadays will carry in their pocket some ferromagnetic material (phone). The speed of processing can only be achieved if individuals do not necessarily have to empty pockets to go through a metal detector.
Using magnetometers, and more specifically fluxgate sensors (as these provide the most appropriate level of sensitivity), you will be able to detect ferromagnetic objects. In some circumstances, it becomes possible to model the source of the anomaly and determine whether it is a threat (weapon) or a day to day object.
Sensors for these applications will need to be as sensitive as possible whilst keeping unit cost down. Power is rarely an issue as mains supply is generally available.
Low cost sensors here would include the Mag612, Mag619 or Mag690.