Robots can express emotions for better human robot interaction. In this field, NAO robot is a platform widely used. This robot mainly expresses emotions by gestures and colored LED eyes, but, due to its white flat and inanimate face, the robot cannot express facial expressions. This work proposes a pluggable eyebrows device enabling NAO to express anger or sadness while performing other tasks. This device is plug-and-play and directly controllable by NAO’s development environments. Additionally, we developed a platform independent mapping of eyebrows angles with emotions. We first conducted an experiment that qualitatively attests the interest of this device. Three following experiments were conducted to: (1) confirm the relation between eyebrows angle and expressed emotion; (2) evaluate different shapes in order to select the most appropriate one; (3) prove that NAO is able to use the eyebrows to express emotions while performing non emotional tasks.