This device had to be able to transmit data over long distances and through several layers of concrete. The battery needed to last weeks without recharging. Finally, the device had to accurately measure the resistivity of the surrounding concrete when it is installed/buried.
Measuring the resistivity of concrete is a well-documented task with a fairly straight-forward method of implementation - namely, a using four-prong voltage and current sensor array. The real challenge is effectively sending data from the device when it is in concrete. Concrete absorbs electromagnetic waves, making standard RF systems difficult to use unless the device is near the surface. Other methods could use pressure waves for data transmission. A secondary device, outside of the concrete, could then be used to pick up small signals from the measuring device and route them over to a central location for analysis.