IoT devices and systems are becoming smaller, faster and their complexity is increasing . In addition, workflow automations and the restructuring and digitalization of business processes are pickung up in speed . Creating a behaviour abstraction of Internet of Things (IoT) systems unlocks benefits such as evaluation of potential design flaws and many more. This is done by creating models of the IoT systems. This thesis discusses how the modelling of IoT systems can be improved to be more intuitive for IoT process modelers. Highlighting existing reference model and different views upon IoT systems, the created reference model uses a distributed systems view upon IoT systems to match the mental model of IoT process modelers. The process modelling language subject-oriented Business Process Management (S-BPM) is evaluated and its suitability to create a behaviour model is shown. The created reference model, based on an existing security use-case, shows how IoT systems can be modelled with a more intuitive approach. Evaluatig the model together with IoT process modelers has shown that the model can increase productivty and reduce modelling times. Furthermore, the reference shows strengths in providig solutions for complex modelling discussions, for example how events can be handeled ad how power states of sensors can be managed. For an easier start with the refernce model the interviewed stakeholders stated that they would prefer a practitioner handbook, which highlights repeatable patterns and how various sensors, and devices can be standardized. Moreover, multiple examples might be necessary to enable process modelling experts to correctly dissect the IoT devices along the three layers.