Data collected in a cruise ship cabin from a monitoring system can be used for various scenarios, such as the energy waste reduction and the passenger wellness & comfort. Although the reference scenarios are out of the scope of this paper, we concentrate on presenting an effective and efficient monitoring system. In this context, we describe an environmental monitoring system for a closed environment, based on heterogeneous sensor networks, and a minimal invasiveness approach for a robust monitoring of sleep quality, which integrates signals from different types of sensors to estimate physiological parameters.