Abstract: An emergency telephone call actuated light signal is visible externally of the building includes a telephone line monitor and a microcontroller for comparing the dialed numbers with a stored emergency number. If the microcontroller detects a match, it emits an actuation signal which causes operation of a light signal visible on the exterior of the building. The microcontroller includes logic for discriminating between a stored emergency number containing a series of digits and a dialed number containing the stored number sequence as a part of greater series of digits.