These buttons are usually represented by buttons or emergency crash bars by pressing which an electronic or magnetic door opens. This is achieved by breaking the power to an otherwise powered device. Motion detectors mounted above doors enabling doors to open when a person approaches them is yet another example of the request to exit devices.
When pushing REX button, pulling a T-bar handle or approaching the range of a REX sensor an individual does not need credentials to leave a building.
Such access control solutions are implemented for easy accessibility within secure areas, in places with people continuously going in or out, in emergency exits or handicapped accessibility.