The invention relates to a trigger unit (1) for attachment to an installation switching device, comprising a coupling apparatus (4) which can take an ON position and a trigger position, and which can be coupled to a trigger apparatus of the installation switching device upon attachment to an installation switching device, wherein the trigger unit (1) comprises a signal current path which contains a hammer armature system (5). Said trigger unit is characterized in that the trigger unit (1) comprises a transmission building block (6), having a movement element (2) which is supported for longitudinal displacement for being coupled to the coupling apparatus (4), a locking member (7) for locking the movement of the movement element (2), a switching member (8) for alternately moving and releasing the movement element (2), a drive member (10) for alternately driving and releasing the switching member (8), wherein the switching member (8) and the locking member (7) are mounted so as to rotate about a common axis and wherein said members can be engaged with the movement element (2), and wherein the drive member (10) can be loaded by the hammer armature system (5) to cause a driving movement.