Internet-of-things does not require that every device has to be directly connected to the Internet. The complexity and possible security issues with every sensor having its own IP address would in fact be overwhelming. A better approach would be to use more light-weight protocols for the sensor and actuator data and locally aggregate and filter these data at common points before making them available on the Internet. In this post I will describe a theory and implementation of transmitting small radio chirp messages from an Arduino Pro mini and then receive these data on a Raspberry Pi for transformation to MQTT messages for the Internet.
This blog post describes how I have set up a door-open detector at home. It uses a small ATtiny85 board that broadcasts a 433 MHz signal every time the door is opened. The signal is fetched by a Raspberry Pi that in turn publishes an MQTT message that results in the event being stored in a database and also being re-published to a cloud service. The circuit is only active when the door is open (and in that state only consumes 10mA), so the whole setup can be driven by a battery pack that is bound to last for a very long time.