The Dexcom G4 is a continuous glucose monitoring system (CGMS) worn by type 1 diabetics. It has a USB port and Windows only software for downloading and analysing data.
A team of developers / users have created an open source realtime remote monitoring, alarm and glucose prediction system for it. It uses a USB OTG cable to connect the Dexcom to a commodity Android phone, which runs a custom Android app to upload the data to MongoLab. From there, a Node.js powered dashboard gives viewers - typically parents of diabetic children - a way to monitor glucose levels remotely. In addition, a Pebble watch app lets the wearer check their glucose by just looking at their wrist, instead of having to use the bulky Dexcom monitor.