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Objective: The purpose of this research was to evaluate the effects of an intervention on reducing sitting time in a professional setting. Methods: The intervention consisted of a group presentation on sedentary behavior at work and active work breaks, followed by an individual planning phase. Participants were then invited to use alert software for four weeks. The intervention lasted six weeks; 38 people aged 29 to 59 years participated (80% women). Before and after the intervention, participants wore accelerometers to assess behaviors (sedentary and physical activity at work) and responded to a questionnaire measuring the degree of automaticity for sitting at work and taking active breaks. Results: After the intervention, the time spent in a sitting position during a working day decreased significantly. Specifically, sitting time decreased more among those aged 29 to 43 years; who had decided to take breaks of at least 5 minutes; and had more extended sitting time before the intervention. Conclusions: This study demonstrated that combining an informational strategy with computer- or mobile-generated alerts reduces sitting time spent in the workplace. This intervention was inexpensive for employees and companies. An interesting perspective could be to compare these effects with those of interventions based on a change in the physical work environment (such as the installation of adjustable desks).