With this device, each party keeps one at home and can control the other’s device. By default, both lights are off. When the kid is home and available for talk, he/she switches the toggle to the right side, which triggers the light on the other end, i.e. in his/her parents home, to white, indicating she/he is available for a chat. Same applies to their parents' device. Whenever they are unavailable, they can switch the toggle to the left and the other’s light will turn on.