How to develop a new Device
Assuming you already have the protocol, you need a device implementation. There are (at least) two possible ways.
A) Implement the new device in Java, like the SensorTag. In this case, you should write one class, inheriting from the base device class (or some more specific class in the hierarchy). Currently, this is included in the DeviceManager of the core, but we are working on moving it out of the core. The target is that you only need to drop a class file
B) Implement the device interface right on the D-Bus, i.e. in whatever language. This is a but more complex, but there are examples for Python.