The application of remote sensing devices (RSD) for on-road vehicle emission monitoring programme helps to screen vehicles on the road to identify gross or very high emitters. Its application requires a national guidance framework to guide cities on its implementation and detail out the full scope of implementation including technology and site selection, system design, data analytics, enforcement strategies, fleet screening, technology feedback system, management of old vehicles, enabling low emissions zones among others. To demystify the key aspects of remote sensing application and its technical complexity this primer is the first step towards informing the national level guidance framework for adoption and implementation of remote sensing measurement system in Indian cities. This primer addresses the frequently asked questions relevant for regulatory and implementing agencies.