Experience Sampling Method (ESM) is a structured diary technique assessing variations in thoughts, mood, and psychiatric symptoms in everyday life. Research has provided ample evidence for the efficacy of the use of ESM in general psychiatry but its use in forensic psychiatry has been limited. Twenty forensic psychiatric patients participated. The PsyMate™ Device emitted a signal 10 times a day on six consecutive days, at unpredictable moments. After each “beep,” the patients completed ESM forms assessing current context, thoughts, positive and negative affect, and psychotic experiences. Stress was measured using the average scores of the stress related items. Compliance rate was high (85% beeps responded). Activity stress was related to more negative affect, lower positive affect, and more psychotic symptoms. This finding was restricted to moments when a team member was present; not when patients were alone or with other patients. ESM can be useful in forensic psychiatry and give insights into the relationships between symptoms and mood in different contexts. In this study activity-related stress was contextualized. These findings can be used to personalize interventions.