A touch sensor configured to be disposed in a liquid crystal display panel includes a plurality of x-axis read-out lines crossing and insulated from a plurality of y-axis read-out lines and a plurality of sensor units. Each sensor unit includes a reset unit, a capacitance detector, a first output unit, and a second output unit. The reset unit outputs a first reset signal based on a first control signal. The capacitance detector changes the first reset signal based on a variation of a cell gap of the liquid crystal display panel caused by a touch event. The first output unit changes an electric potential of a corresponding x-axis read-out line in response to the first reset signal changed in the capacitance detector. The second output unit changes an electric potential of a corresponding y-axis read-out line in response to the first reset signal changed in the capacitance detector.