John Pistole, the chief of the Transportation Security Administration (TSA), often refers to random patrols or inspections as a key element of his agency's security strategy at US airports.

As recently as March 14, 2013, Pistole told the House Committee on Homeland Security that "TSA will always incorporate random and unpredictable security measures throughout the airport" to make it difficult for terrorists to observe patterns in security measures and thereby evade them.

However, there is another key motivator for randomizing security measures -- limited resources...