They sense movement via sound, and then send an alert to that effect to monitoring station X.
It's not as though they're collecting any sensitive data, and it's not as though they could be used to actually spy on people..yet.
This would be excellent perimeter control for secure military installations and other controlled-entry areas. They're inconspicuous and don't draw attention like standard surveillance equipment does.
I can see these being used to great effect by security companies in America. They even have potential for use by private citizens, for example, to alert them to burglaries when they're away from home. Or even better, parents could use them in the driveway to make sure their kids aren't partying when the folks go on vacation, if you hear a bunch of cars and foot traffic, you know something's up.
In the current incarnation I think they're particularly well suited for use along the Mexican border. This is nifty technology, thanks for posting it.
The one flaw I see is that they could easily be jammed, to prevent transmission of particulars, like the number of people running through the area. If they get jammed, the monitoring station is obviously going to know something's up, but still, they won't be able to discern what, without some form of back-up system.
