Abstract: A replacement elevator call button unit which may be electrically connected to an elevator controller having first and second power supply lines and having an elevator call registering terminal. The replacement unit includes an electronic switch (preferably a silicon controlled rectifier) which is electrically connectible between the power supply lines. A normally open push button is electrically coupled to the switch in order to switch the first switch from an inoperative state in which current flow between the power lines is prevented, to an operative state in which such current flow is permitted. A voltage divider is provided for electrical connection across the elevator call registering terminal, in series with the switch means. Cross firing between two or more corresponding replacement units is accomplished by a second electronic switch (preferably a photo diode) optically coupled to the first switch, without requiring any additional wiring.