Harmony Chairs are interactive rocking chairs that produce sounds in response to rocking motion and synchronization. In modern public spaces, spontaneous interaction among strangers has diminished as people increasingly focus on their personal devices. Harmony Chairs aims to revive such interactions by offering a playful and shared experience. This interactive installation consists of three rocking chairs, equipped with accelerometers and speakers, and designed to respond to users’ movements. Each chair has a unique set of pitches assigned to it. When a person rocks a chair individually, it produces soft, soothing sounds, still the real magic happens when users begin to interact with each other. As two or more users synchronize their movements, the chairs generate distinct bell-like tones that are clear and harmonious. This auditory feedback encourages users to align their movements, creating a shared goal and fostering a sense of connection, turning strangers into collaborators.