A power module is configured to accept power from a cable, wherein the power module may be inserted into a standard wall cavity via a small hole. A processor module coupled to the power module comprises a processor and is configured to accept power from the cable for the processor, wherein the processor module may be inserted into the standard wall cavity via the small hole. A sensor module coupled to the processor module, comprises a sensor and is configured to accept input from the sensor for the processor, wherein the sensor module may be inserted into the small hole.