Two-way switches to control a load from two different places (stairs-switch)
A two-way switch allows a device to be switched on or off from two different locations. The most common example is found in houses where you have a switch at the bottom of the stairs and another at the top, allowing you to switch the light on or off from either the top or bottom of the stairs.
Instalation diagram for two-way switches:
Simulation for two-way switches circuit in program EWB Electronics Workbench