A dimmer switch coupleable to a circuit including a power source, load, and single-pole double-throw three-way switch that comprises a first and a second fixed contact and a movable contact. The three-way switch has a first state and a second state. The dimmer switch comprises first, second and third load terminals coupled in series with the three-way switch. The dimmer switch comprises a controllably conductive device. A sensing device is coupled to the third load terminal such that when the three-way switch is in the second state, the sensing device is operable to sense an electrical characteristic associated with the third load terminal. A controller is coupled to the controllably conductive device and to the sensing device for rendering the controllably conductive device conductive in response to the sensed electrical characteristic and so that power is delivered through the second load terminal of the third load terminal depending on the state of the three-way switch.