Remote Sensing using infra-red technology can detect tailpipe emissions with minimum public inconvenience. There have been several studies that have evidenced the basic accuracy of the technology. Other studies have tested the potential of the technology as an alternative or supplement to traditional smog inspections or enhanced I/M. The results from these have shown that at normal I/M emissions standards significant errors of commission (false failures) occur. This paper reviews the results of three studies from the perspective of limiting use of the device to identify only gross emitters, which are major contributors to total mobile emissions. It finds that a significant fraction of gross emitters can be identified with a low rate of false failures and minimum inconvenience to the public. Remote Sensing Technology can usefully complement basic or enhanced I/M programs by identifying vehicles that deteriorate between the standard I/M inspections, identifying vehicles that are deliberately or accidentally tampered, and identifying vehicles that may be evading the I/M program through incorrect registration or other means.