Each stair is tethered by springs and equipped with pressure sensors. When a person walks downstairs, each step slowly sinks until it locks into place and is level with the next step, storing energy generated by the user. It stays that way until someone walks upstairs. When a person ascending the stairs steps on the sensor on the next tread up, the latch on the lower step releases. The stored energy in the spring is also released, lifting up the back leg.