We’ve decided to go with mesh networking for the sensors to help bring the cost down. As it turns out, a significant portion of the cost of a sensor comes from its on-board wifi, so we thought, why have all the sensors in the building use wifi? Why not have most of them use something really cheap, like short-wave radio, and then let them all talk to one broadcasting base that communicates with our servers on behalf of all of them? Turns out, that’s called mesh networking, and it cuts our costs by around 50%. There’s a fairly easy solution for radio-wave based mesh networking out there called XBees - we’re looking into it.