A certain level of stress is crucial for survival; however, prolonged exposure to stress may have negative health consequences. Smartwatches are a practical tool to monitor the body’s arousal state by measuring autonomic nervous system activity in daily life, commonly referred to as stress levels by the smartwatches. How these stress levels relate to emotional states, however, remains unclear. This study aimed to investigate the association between the Garmin Stress Score and both negative and positive emotional states of varying intensity. Over 28 days, Ecological Momentary Assessment (EMA) data were collected five times a day for emotional states, and Garmin Stress Score data were collected continuously, in a sample of 95 (80F) healthy young adult university students in the Netherlands. Binary and linear multilevel models were used to associate the Garmin Stress Score with the presence of emotions, and a dose-response relationship, respectively. The Garmin Stress Score was associated with high- and moderate-intensity positive emotions but not with negative or low-intensity emotions. The emotions ”calm” and ”relaxed” showed a negative dose-response relationship with average Garmin Stress Score, and a positive trend was found for ”enthusiastic.” Since the Garmin Stress Score relies on parasympathetic activation, representing the rest-and-digest state, rather than fight-or-flight, it makes sense that it is associated with states of non-relaxation. However, it was not associated with states of high arousal negative affect. This makes the term ”Stress Score” incorrect and misleading to consumers. Our findings warrant further research into emotional states, particularly those associated with high arousal negative affect. We recommend stronger collaborations between commercial companies like Garmin and researchers to enhance the accuracy of feedback provided by wearable devices and mitigate any harmful effects on consumers.