Steve (aka Polymythic) created a Motion Feedback MP3 Player that plays music tracks at varying volume depending on the level of activity the system detects. The concept is to encourage more activity by creating a feedback loop between the volume of music and the level of your activity.
Motion is detected with a Parallax PIR Sensor. When motion is detected, the output pin of the sensor goes high. That out is monitored by the ioBridge IO-204. With or without a network connection, the IO-204 sets the volume of a DIY MP3 Trigger board from SparkFun. The volume is controlled by sending serial strings to the MP3 Trigger. Steve took advantage of the new Onboard Rules that turn the IO-204 into a standalone controller. When the IO-204 is connected to the Internet, the IO-204 also data logs his activity by sending it to the ioBridge data logging service in the cloud.