A capacitive sensor device has at least one measuring electrode, at least one ground electrode, and an evaluation device being coupled with the at least one measuring electrode and being configured to detect a capacitive coupling between the at least one measuring electrode and a ground of the evaluation device.At least one ground electrode can be galvanically coupled with the ground of the evaluation device via a switch. The switching status of the switch can be changed by the evaluation device. The evaluation device is further adapted to detect a common-mode change of the capacitive coupling between the at least one measuring electrode and the ground of the evaluation device when the switching status of the switch changes. An input device, particularly a keyboard with a capacitive sensor device, as well as a method for operating a capacitive sensor device may be designed accordingly.