Would it not just work as a Faraday cage?

Mobility
    What types of environment can they move about in? Desert? Shallow water? Everything in between?
    Are they small turtles or could the design be made self-righting?
Communication - Range? - Algorithm to leave a trail of relay bots for longer ranges?
Sensors
    Just touch? Basically just mapping then.
    Could they maybe have sensors for sniffing out explosives?
    Images? - Should a paranoid person worry if they find a few of those near a window?
Pollution - Do they contain heavy metals or other toxins?
Cost - When might these things be cost effective to deploy, say in Afghanistan?