I have changed the title to get this going as a separate discussion. What you are asking is a topic that has been discussed for quite a while. The concept is "service processor". We envision roles of the service processor could include reporting battery voltage, control or restart 12v or 120v devices, GPS location using APRS over the network, weather, and similar. WB5AOH has a proto of a board he has demonstrated. There are several approaches to this. The Austin QRP group (on Yahoo) is actively developing the Arduino kits. This motor control daughter board http://www.makershed.com/product_p/mkad7.htm along with the Arduino host board would be the basis for turning things on and off. The basic Arduino kits can directly sense voltages. All that is needed is a bit of programming to pull the outputs and submit them as data traffic. "developers welcome".