The apparatus and method for detecting aerosol includes transmitting a light beam, focusing at least one image sensor having a field of view that encompasses at least a portion of the light beam on a portion of the light beam, capturing an image of the light beam by the image sensor(s), and detecting aerosol if the image of the light beam has a predefined shape and at least a predetermined intensity. Therefore, the apparatus and method for detecting aerosol permit the accurate detection of aerosol, while ignoring the stray contaminants that routinely cause false alarms in conventional aerosol detectors. In particular, an image of a light beam is sensed when aerosol is present, such that random contaminants that adhere to the walls of a detection chamber or that pass through the light beam do not affect the aerosol detection.