In this short course, you will discover how the integration of biofeedback data makes it possible to evaluate the user experience in immersive environments. We will explore fundamental concepts of virtual and augmented reality and understand how biofeedback data can provide insights into user behavior and reactions in immersive experiences. At the end, we will do a practical demonstration analyzing heart rate and eye tracking data from two immersive simulations: the interior of a vehicle (complementary video available at https://youtube.com/shorts/zHAiAgCsu4g) and activities at height on the façade of a building, using devices such as Pico 4 Enterprise, Hololens 2, Meta Quest Pro or Quest 3 and Samsung 7 smartwatches.