Pre-deployment tests of sensor networks in indoor testbeds can only deliver a 
very approximate view of the correctness and performance of a deployed sensor 
network and it is therefore common that after deployment problems and failures 
occur that could not be observed during pre-deployment tests. Finding and 
fixing such problems requires visibility of the system state, such that an 
engineer can identify causes of misbehavior. Unfortunately, exposing the 
internal state of sensor nodes requires resources such as communication 
bandwidth and energy: the better visibility of system state is required, the 
more resources are needed to extract that state from the sensor network. In 
this paper we propose a concept and tool that give the user explicit control 
over this tradeoff. Essentially, the user can specify a resource budget and 
our tool strives to provide best possible visibility while not exceeding the 
resource budget. We present the design of our vLevels framework and report the 
results of a case study demonstrating that the overhead of our approach is 
small and that visibility is automatically adjusted to meet the specified 
resource budget.