This ultra-flat flush-mounting unit is finished in 3 mm-thick aluminium and can be easily integrated into a wall or partition. 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. This external unit works with 2-wire technology, which means that an existing bell can simply be replaced by a similar external unit. The external unit includes the flush-mounting box. This external unit has 1 bell. From 12 bells, the bell buttons are arranged in two rows and from 24 in three rows.