Handy post from DIYhacking.
This Raspberry Pi IoT project is the best way to get started on working with the IoT (Internet of Things) and to build your knowledge to expand it to other applications. The first problem was figuring out a simple enough sample project to learn how to make sensors communicate with each other. So, we made a step-by-step guide for Pi beginners so they can learn various methods that can be used to make their application of choice.
In short, we use the Raspberry Pi to record temperature on a trigger and then push notifications from the server to your Android device.