1. A method for detecting operator alertness of an operator of a vehicle or machine, the method comprising: collecting reference position data associated with an operator when the operator is in an alert state; determining observed position data of one or more reference points of a three dimensional representation of the operator, or a portion thereof, during a time interval; and sending an alert signal to alert the operator if a detected angular shift of one or more reference points, associated with an operator, exceed a displacement threshold.