In this thesis, I propose NICE (Natural Intuitive Camera-based Environment) control which allows occupants to use freehand-gestures, speech commands and a multimodal combination of both in order to interact with individual devices in a smart building. The usage of gestures and speech is a natural user interface that allows for an easy and intuitive interaction. Backed by a 3D camera, users can interact from various positions in a room without any additional personal device. The development of NICE control was complemented by two dedicated user studies as well as a continuous quasi-experiment in a user-centered approach. The first, a wizard-of-oz study, provided essential findings for the design of gestures and speech commands, whereas the second user study evaluated the real-world performance of NICE control. Participants stated they enjoyed natural user interfaces for controlling a smart room and were able to complete about 90% of the given tasks. Speech showed the fastest overall completion times for the tasks. Notably, participants ranked gesture commands as fastest and most fun.