Internal electrical armor to prevent cargo thieves. It is capable of causing an electric discharge of 20 thousand volts only when a drilling occurs for the attempted break-in.
The electric shock is not lethal, but certainly strong enough to keep the thugs away from the cargo truck.
It poses no risk to workers and passers-by because the vehicle always moves with the electrification deactivated. Activation will be automatic if, and only if, attempted breach occurs.