Laser power monitoring arrangements interrupt power to a laser used in electro-optical readers upon detection of operating conditions not conforming to preestablished standards. An auxiliary light detector independently monitors the output power of a laser beam, and directly receives a portion of the laser beam reflected from a diffractive optical lens surface of an optical assembly for optically modifying the laser beam, or from a coated or uncoated inclined surface of a split collimating lens of the optical assembly. The split collimating lens may have its lens portions in mutual contact or separated by an air gap.