Presence detection and occupancy monitoring constitute enabling technologies for both space analytics and energy-aware building operation. However, when sensing nodes are battery-powered, the achievable system value is constrained by lifetime, which depends on the interaction between firmware duty-cycling, sensing workloads, wireless communication patterns, and battery discharge dynamics. This thesis addresses the simulation and validation of embedded systems for presence detection by developing an energy modeling framework for Dropper MINI, a compact battery- powered sensing node designed for anonymous occupancy monitoring. The platform integrates a multi-zone Time-of-Flight sensor, an infrared presence sensor, and an ambient light sensor with light-flicker extraction capabilities, enabling both occupancy-related analytics and lighting-condition assessment.