This is still a work-in-progress, but here's the current featureset:
* An ultrasonic sensor (HC-SR04) is mounted behind the toilet, and can sense the presence of a person, and determine if they are sitting or standing.
* This sensor is periodically monitored by an Electric Imp which determines if the toilet is in use and updates a webpage.
* The setup is powered by a LiPo battery and is USB rechargable. The goal is to have a long enough battery life that it can be recharged no more than once every few months.
* Have a second Imp implement a "traffic light" system that can be mounted near the toilet or elsewhere in the office and indicate whether the toilet is occupied or free.
* Make a fancy web interface complete with metrics and infographics, and possibly #slack integration.
* Depending on how low we can get the power usage, we might try to make it solar powered like some of those fancy automatic sinks.