The $1.2 billion for border security is designated for a traditional fence, vehicle barriers and a so-called virtual fence made up of cameras and sensors.

Software allows parents to establish a virtual fence, sending an alert if the child strays beyond authorized areas while wearing the pack.

In a similar system, the collar uses GPS signals to determine proximity to a predetermined "virtual fence" without a physical installation.

Michael Chertoff, announced that an eight-month test of the virtual fence, he favors, will precede any construction of a physical barrier.

At completion, Boeing estimates that it will use approximately 1,800 towers to create its "virtual fence" along the borders.

Quite a few thieves have looked at on-line auction sites and seen the perfect virtual fence, the way to sell their stolen property.

This year, both programs sport improved interfaces, and both programs are swinging for the virtual fences with their Internet links.

In another type, the collar uses GPS signals to determine proximity to a predetermined "virtual fence", without the need for any physical installation at all.

Homeland Security agencies have been pursuing separate communication projects, citing Congressional pressure to create a high-tech "virtual" fence on the Mexican border.

It authorizes the building of a 700-mile fence, or the deployment of electronic devices and drone aircraft to create a "virtual fence."