A substantially automatic, robotic-like system to aid in preventing crime in high trafficked buildings and other public sites, using only low voltage power, is described. In various modes it can protect public buildings such as schools, stadiums, open air markets, banks, office buildings from entrance of persons carrying weapons or separately trying to pass weapons into a protected area, even in the event of general power loss. Here a well designed, compact solution is provided for weapons detection and the detainment of persons attempting to disrupt, destroy or harm citizens in public buildings such as schools, banks, etc. with a minimum of restriction of access by persons regularly using the facilities. In other variations, it can be used to prevent unauthorized removal of costly or dangerous items from protected buildings or areas. Here a substantially automatic method is similarly provided for detection and detention of persons attempting to illegally remove items either without paying or that are not for sale in a store setting.