Encoder-less lidar positioning technique for detection and alarm

An apparatus comprising:

• a detector unit;
• a rotational laser beam driven by a motor;
• memory having instructions stored thereon that, when executed, cause the apparatus to:
• distribute light during a first instance of time in order to characterize an area being monitored based on first data associated with the first instance of time, wherein a characterization of the area is based on a determination of a position of a rotational laser beam;
• distribute light during at least a second instance of time in order to obtain second data;
• compare at least a first portion of the second data to at least the first data;
• and
• based on the comparison, signal an alarm condition when an evolution in the second data is detected in an amount greater than a threshold;
• wherein the instructions, when executed, cause the apparatus to determine a position of the rotational laser beam by applying phase correlation with two sequential data sets obtained by the detector unit.