Building automation device which can be recessed in an electrical box, comprising a communication module with a communications bus (1.1) of the device, an application module that implements the functionality of the device, and a bus connector between the two modules (1,2), characterised in that said bus connector is for power supply and data transfer, the communication module comprising a first base (1.2) comprising at least four first side faces (1.21), closed on one of its sides by a first rear cover (1.22), creating a first cavity (1.23), leaving on the other side a first opening (1.24), the rear cover (1.22) having a second opening (1.25) through which the communications bus (1.1) passes, at least two first protrusions (1.26), each one of them on different side faces (1.21), at least one first flange (1.27) on one side face (1.21), at least two second protrusions (1.28), each one of them on different side faces (1.21), from the first opening (1.24) the second protrusions (1.28) are arranged upstream of the first flange (1.27) and the latter upstream of the first protrusions (1.26), on the first protrusions (1.26) a first printed circuit board (1.3), retained by the first flange (1.27) is supported, on the second protrusions (1.28) a second printed circuit board (1.4) is supported to which the communication bus (1.1) is connected and from which at least ten pins (3.1) of the bus connector project, a first front cover (1.5) with a third opening (1.52) for the passage of the at least ten pins (3.1), a support plate (1.6) arranged surrounding the side faces (1.21) to the vicinity of the first opening (1.24), the application module comprising a second base (2.1) comprising at least four second side faces (2.11), closed on one of its sides by a second rear cover (2.12), creating a second cavity (2.13), leaving on the other side a fourth opening (2.14), a first frame (2.15) surrounding it, the second rear cover (2.12) having a fifth opening (2.16), when at least two third protrusions (2.17), each one of them on different side faces (2.11), at least one second flange (2.18) on one side face (2.11), at least two fourth protrusions (2.19), each one of them on different side faces (2.11), at least one third flange (2.20) on one side face (2.11), from the fourth opening (2.14) the first frame (2.15) is arranged upstream of the third flange (2.20), the latter upstream of the fourth protrusions (2.19), the latter upstream of the second flange (2.18) and the latter upstream of the third protrusions (2.17), on the third protrusions (2.17) a third printed circuit board (2.2) is supported to which the receiving connector (3.2) is connected, retained by the second flange (2.18), on the fourth protrusions (2.19) a fourth printed circuit board (2.3) is supported retained by the third flange (2.20), a fifth printed circuit board (2.4) is supported on the first frame (2.15), in use when the ten pins (3.1) of the bus connector are introduced in the receiving connector (3.2) that passes through the fifth opening (2.16), the second side faces (2.11) are introduced in the first opening (1.24), and the first base (1.2) is joined to the second base (2.1) via attachment means (1.29,2.21).