The Sensor Technology Adapter Gateway (STAG) is an open source project aiming on the ease of integrating sensor systems. Smart sensor systems are one of the central aspects of a smart factory respectively Industry 4.0. However, separate sensor systems from various vendors frequently use different or even proprietary communication protocols. This can cause complications, when integrating all of these systems into a common communication protocol or even an Internet of Things Platform (IoT). It gets even more complicated when the same sensor systems need to be integrated to separate parallel IoT platforms or databases to support different use cases. For example, an IoT Platform to monitor the real time state of various sensor systems and a separate database optimized to store statistical data from the sensor systems for a predictive maintenance system. The modular sensor adapter gateway STAG reduces the integration complexity by abstracting various different sensor communication technologies and protocols with an unified informatione model combined with an automated data mapping. Furthermore, STAG can be easily scaled by adding new sensor adapters without having to manually expand the IoT Platform models as well as providing a simple interface for future IoT solution integrations.