A new method of determining continuumbreakdown in hypersonic flows that is part of a modular particle-continuum numerical method is presented. The modular particle-continuum method loosely couples direct simulation Monte-Carlo and Navier-Stokes methods which operate in different regions, use different mesh densities, and are updated using different sized timesteps. The hybrid method includes overlapping regions where both particle and continuum methods are used. The new method of detecting continuum breakdown involves the direct comparison of particle and continuum solutions within such overlapping regions. Such a method of continuum breakdown detection eliminates the use of a breakdown parameter and associated empirical cutoff value used in the majority of prior hybrid research. Hybrid simulations of hypersonic flow over a cylinder using this new method are shown to accurately reproduce the flowfield properties and heating rates of full DSMC simulations. The new method of continuum breakdown detection is more computationally expensive than computing a breakdown parameter and is more sensitive to statistical scatter.