Abstract: A sub-surface laser scanning device is disclosed. The device employs laser pulses to scan an entire area of a swimming pool and uses that scan to constantly compare to current conditions in the pool in order to determine if a person has actually submerged below the surface of the pool. Entry of an object or person in the pool disrupts the laser pulses and triggers an alarm. The device may be set up to detect pool equipment and other common pool items, in order to avoid triggering false alarms.