A system for monitoring the movement of people or objects through a passageway comprising: - two or more time of flight ranging sensors deployed across the passageway in a direction substantially transverse to the direction of movement of a person or object through the passageway, wherein each time of flight ranging sensor is arranged to: - transmit a single beam of light; and - receive a signal which is reflected from an illuminated area on a person or object intersecting the path of the transmitted beam; - means to measure the time of flight of each sensed reflected signal, which is indicative of the distance from the sensor to a person or object passing through the passageway, the system further comprising: - means to determine the speed at which a person or object moves through the passageway; and - means to determine the number and direction of people or objects passing through the passageway based on the time of flight signals measured by the two or more sensors; wherein: - at least two of the sensors are located on opposing sides of the passageway and transmit single beams in generally opposing directions across the passageway; and - each sensor is configured to measure a series of one-dimensional distance data points over intervals of time, the system further comprising means to combine the one-dimensional distance data points within each series with the determined speed at which the person or object moves through the passageway to create a two-dimensional cross-sectional profile of a person or object passing through the passageway relative to each sensor. - two or more time of flight ranging sensors deployed across the passageway in a direction substantially transverse to the direction of movement of a person or object through the passageway, wherein each time of flight ranging sensor is arranged to: - transmit a single beam of light; and - receive a signal which is reflected from an illuminated area on a person or object intersecting the path of the transmitted beam; - transmit a single beam of light; and - receive a signal which is reflected from an illuminated area on a person or object intersecting the path of the transmitted beam; - means to measure the time of flight of each sensed reflected signal, which is indicative of the distance from the sensor to a person or object passing through the passageway, - means to determine the speed at which a person or object moves through the passageway; and - means to determine the number and direction of people or objects passing through the passageway based on the time of flight signals measured by the two or more sensors; - at least two of the sensors are located on opposing sides of the passageway and transmit single beams in generally opposing directions across the passageway; and - each sensor is configured to measure a series of one-dimensional distance data points over intervals of time, the system further comprising means to combine the one-dimensional distance data points within each series with the determined speed at which the person or object moves through the passageway to create a two-dimensional cross-sectional profile of a person or object passing through the passageway relative to each sensor.