Adequate hand hygiene is the most effective method to reduce the risk for patients of acquiring healthcare-associated infections. However, compliance with hand hygiene guidelines is alarmingly low in healthcare facilities around the world. Both refining knowledge by providing feedback on past behavior and targeting social norms are promising approaches to improve hand hygiene behavior and, in turn, reduce the infection risk in hospitals. In the present field experiment, an electronic monitoring and feedback device was installed on top of the alcohol-based hand-rub dispenser in eight hospital patient rooms for a period of 17 weeks. In the experimental condition, these devices provided instant feedback about the current hand hygiene status by presenting emoticons (i.e., a frowny or a smiley) via a small monitor. Based on previous literature, it was assumed that the emoticons would trigger injunctive social norms (i.e., I should do what ought to be done). Whenever a person passed by the dispenser, a frowny face was displayed, which indicated that hand hygiene should be performed. If the dispenser was subsequently used, the picture changed to a smiley face to positively reinforce the desired behavior. The hand-rub dispensers in the emoticon condition were used significantly more often than the dispensers in three control conditions. The present intervention is the first to examine the effect of activating injunctive norms via emoticon-based feedback on hand hygiene behavior in a hospital. The results of this applied research indicate that knowledge activation and targeting injunctive norms may be a promising approach to reduce noncompliance with hand hygiene guidelines and possibly other risky health behaviors. Theoretical and practical implications of these findings are discussed.