Assembly unit which accommodates within a housing - an electronic circuit unit which can be electrically connected to a higher-level switching system for signal and power supply and has a signal processing unit for controlling consumer elements which are connected to the assembly unit or are installed within the housing, comprising: - a mechanical securing and unlocking element movably held on the assembly unit for mechanically securing and unlocking the electronic circuit unit in a state electrically connected to a higher-level switching system, - the securing and unlocking element being movable relative to the assembly unit between at least two positions manually from outside the assembly unit, - a movement detection device arranged on the assembly unit, which is designed to detect a relative movement of the securing and unlocking element, wherein the movement detection device is designed to generate an unlock signal and to forward it to the signal processing unit in response to a relative movement from a first position, in which the electronic circuit unit is completely mechanically secured in the electrically connected state, into a second position in which the electronic circuit unit is at least partially mechanically unlocked in the electrically connected state,, the signal processing unit being designed to switch consumer elements which are under load load-free in response to the unlock signal by means of generating at least one load disconnection signal, so that complete disconnection of the assembly unit with load-free electronic circuit unit from the higher-level switching system is possible during ongoing operation. - an electronic circuit unit which can be electrically connected to a higher-level switching system for signal and power supply and has a signal processing unit for controlling consumer elements which are connected to the assembly unit or are installed within the housing, comprising: - a mechanical securing and unlocking element movably held on the assembly unit for mechanically securing and unlocking the electronic circuit unit in a state electrically connected to a higher-level switching system, - the securing and unlocking element being movable relative to the assembly unit between at least two positions manually from outside the assembly unit, - a movement detection device arranged on the assembly unit, which is designed to detect a relative movement of the securing and unlocking element, wherein the movement detection device is designed to generate an unlock signal and to forward it to the signal processing unit in response to a relative movement from a first position, in which the electronic circuit unit is completely mechanically secured in the electrically connected state, into a second position in which the electronic circuit unit is at least partially mechanically unlocked in the electrically connected state,, the signal processing unit being designed to switch consumer elements which are under load load-free in response to the unlock signal by means of generating at least one load disconnection signal, so that complete disconnection of the assembly unit with load-free electronic circuit unit from the higher-level switching system is possible during ongoing operation.