The invention relates to a building automation device adaptable to space and communication requirements, comprising a communications module having a communications bus, an application module which implements the functionality, a bus connector for supplying power and data between the two modules, the communications module comprising a first casing having a first wall from which pins of the connector bus project, and a second wall with a first recess in which the communications bus is inserted, the application module comprising a second casing having a third wall from which a pin receiver projects, and a fourth wall having a second recess including electrical connection terminals, wherein, when the ten pins of the bus connector are introduced in their receiver, the first wall is positioned next to the third wall and the first casing is joined to the second casing by securing means.