Modular communication device for an industrial automation system comprising - a basic module and at least one expansion module that can be connected to the basic module, wherein - the basic module and the at least one expansion module have multi-pole plug connecting elements that correspond to one another, - centring pins are provided on the expansion module, said centring pins each being able to be inserted into a recess on a slotted locking guide of the basic module and being able to be latched there, - the centring pins each have a circumferential groove attached to a conical head, into which groove in each case a latching element of the slotted locking guide engages in a locked state, - the slotted locking guide can be moved perpendicularly to the centring pins from a locking position into an unlocking position, in which the latching elements of the slotted locking guide release the grooves of the centring pins, wherein the slotted locking guide is elastically prestressed in the locking position, as a result of which the slotted locking guide can return from the unlocking position back into the locking position after insertion of a centring pin, characterized in that - the latching elements of the slotted locking guide each have a tapered first contact surface for the conical head of a centring pin, said first contact surface, when a centring pin is inserted through contact with the conical head of the centring pin, causing the slotted locking guide to move into the unlocking position, - the slotted locking guide has tapered second contact surfaces in each case for a conical head of a centring pin, said second contact surface, when the slotted locking guide moves from the locking position into the unlocking position through contact with the conical head of the respective centring pin, causing the centring pin to be pushed out of the respective recess on the slotted locking guide. - a basic module and at least one expansion module that can be connected to the basic module, wherein - the basic module and the at least one expansion module have multi-pole plug connecting elements that correspond to one another, - centring pins are provided on the expansion module, said centring pins each being able to be inserted into a recess on a slotted locking guide of the basic module and being able to be latched there, - the centring pins each have a circumferential groove attached to a conical head, into which groove in each case a latching element of the slotted locking guide engages in a locked state, - the slotted locking guide can be moved perpendicularly to the centring pins from a locking position into an unlocking position, in which the latching elements of the slotted locking guide release the grooves of the centring pins, wherein the slotted locking guide is elastically prestressed in the locking position, as a result of which the slotted locking guide can return from the unlocking position back into the locking position after insertion of a centring pin, - the latching elements of the slotted locking guide each have a tapered first contact surface for the conical head of a centring pin, said first contact surface, when a centring pin is inserted through contact with the conical head of the centring pin, causing the slotted locking guide to move into the unlocking position, - the slotted locking guide has tapered second contact surfaces in each case for a conical head of a centring pin, said second contact surface, when the slotted locking guide moves from the locking position into the unlocking position through contact with the conical head of the respective centring pin, causing the centring pin to be pushed out of the respective recess on the slotted locking guide.