These devices will last at least 20 years and so many were produced that the entire country can be bugged.
The interesting about these “bugs” is that the US forces can’t listen in the remote surroundings but they can only detect movement. Besides being disguised as a rock sensors can also be buried or disguised as other artifacts.
The Department of Defense has money to burn as one of these devices costs no less than $1000. The price is considered a fair one considering the fact it can provide two decades of uninterrupted information.
