Electronic smoking device comprising: a power supply/atomizer portion and a replaceable liquid reservoir portion which is coupleable with the power supply/atomizer portion, wherein the liquid reservoir portion comprises a liquid reservoir storing a liquid and the power supply/atomizer portion comprises a power supply and an atomizer adapted to atomize the liquid stored in the liquid reservoir when operated by the power supply, characterized in that the electronic smoking device further comprises a liquid reservoir portion detection device (50, 54, 46, 48) including, in the power supply/atomizer portion, a liquid reservoir portion detection element that is moveable between a first position and a second position, and an activation element that is adapted to be operated by the liquid reservoir portion detection element when the liquid reservoir portion detection element is moved from the first position to the second position, and in the liquid reservoir portion, a cavity and an engaging element, wherein the cavity is empty and an opening of the cavity that faces the power supply/atomizer portion when the liquid reservoir portion is coupled with the power supply/atomizer portion is at least partially blocked by the engaging element as long as the liquid reservoir portion is not coupled with the power supply/atomizer portion, and wherein the cavity is adapted to receive at least part of the liquid reservoir portion detection element and the engaging element is adapted to engage with the liquid reservoir portion detection element when the liquid reservoir portion is coupled with the power supply/atomizer portion, wherein the liquid reservoir portion detection element is adapted, when the liquid reservoir portion is coupled with the power supply/atomizer portion, to engage with the engaging element so as to be moved from the first position to the second position, thereby operating the activation element. a power supply/atomizer portion and a replaceable liquid reservoir portion which is coupleable with the power supply/atomizer portion, wherein the liquid reservoir portion comprises a liquid reservoir storing a liquid and the power supply/atomizer portion comprises a power supply and an atomizer adapted to atomize the liquid stored in the liquid reservoir when operated by the power supply, characterized in that the electronic smoking device further comprises a liquid reservoir portion detection device (50, 54, 46, 48) including, in the power supply/atomizer portion, a liquid reservoir portion detection element that is moveable between a first position and a second position, and an activation element that is adapted to be operated by the liquid reservoir portion detection element when the liquid reservoir portion detection element is moved from the first position to the second position, and in the liquid reservoir portion, a cavity and an engaging element, wherein the cavity is empty and an opening of the cavity that faces the power supply/atomizer portion when the liquid reservoir portion is coupled with the power supply/atomizer portion is at least partially blocked by the engaging element as long as the liquid reservoir portion is not coupled with the power supply/atomizer portion, and wherein the cavity is adapted to receive at least part of the liquid reservoir portion detection element and the engaging element is adapted to engage with the liquid reservoir portion detection element when the liquid reservoir portion is coupled with the power supply/atomizer portion, wherein the liquid reservoir portion detection element is adapted, when the liquid reservoir portion is coupled with the power supply/atomizer portion, to engage with the engaging element so as to be moved from the first position to the second position, thereby operating the activation element.