Systems and methods for detecting or following a person within an observed area. One example system includes a sensor and a processor configured to: receive, from the sensor, a series of readings indicative of the person in the observed area, wherein the observed area is divided into a plurality of zones; determine a sequential occurrence of each of a plurality of ordered events by applying a detection threshold value to the series of readings, wherein the detection threshold value is lower than a noise threshold of the sensor, and wherein each of the plurality of ordered events is associated with at least one of the plurality of zones; and determine a trigger condition based on the sequential occurrence of each of the plurality of ordered events; and provide an instruction to a fixture based on the trigger condition.