This is some basic php code that checks a pachube data feed for data about a room's power consumption, looks to see if it's above a threshhold, and responds with a a simple html page telling you if anyone's in the room (and using an above-baseline amount of power)

We're getting our power data via a current sensor that Julian Lee clipped around the power mains in the building, and he put in an arduino with a ethernet shield to send the data periodically to pachube.

Here's the tech specs:

1. Power consumption of the space, based on the design from openenergymonitor.org, using a SCT-13-000 clip-on CT sensor attached to the main fuse box. (Code courtesy of openenergymonitor.org)
2. Temperature and humidity of the space, using a DHT11 digital temperature sensor. (Code courtesy of sheepdogguides.com)

And here's our pachube feed: https://pachube.com/feeds/34432