SPAN (Self-Powered Ad-hoc Network) s billed as a "covert, perpetually self-powered wireless sensor network" that provides "unobtrusive, continuous surveillance".
In practice this is a network of "self-organising, self-healing sensors" that can be used to monitor sensitive areas and alert users when something is awry.
This can take many forms. The area in question could be a border, oil pipeline or somewhere deep inside enemy territory.
An alarm could cue a camera or unmanned aerial vehicle to further study an area or call an engineer if something needs repaired.
The hope is the devices can negate the need to constantly have a (costly) human presence in sensitive areas.
Spy rocks have been around for a while but not with this level of sophistication.
Last year Jonathan Powell, former chief of staff to prime minister, Tony Blair, admitted that the Russians had uncovered a plot to spy on them using a device concealed in a fake plastic rock way back in 2006.
He said: "The spy rock was embarrassing.
"They had us bang to rights. Clearly they had known about it for some time and had been saving it up for a political purpose."