This compact surface-mounting unit in aluminium has a surface-mounting height of only 16 mm 20 mm. The external unit is equipped with a 5 mm-thick name plate in Plexiglas which is vandal proof. The metal-plated push-button contacts are maintenance-free and durable. With its double row of bells, this surface-mounting unit is extremely well-suited for large residential complexes. This external unit has 4 bells in two rows.