Identification of North American microchiropteran bat species at roost sites, especially in urban or suburban environs, is challenging. Capture and acoustic detection methods are effective, but only when bats are present, and can result in disturbance to wildlife. Analysis of guano or other physical cues can be effective, but only when present. We investigated the efficacy of genetic analysis of residues left directly on roosting surfaces. At two sites in Northern California roosts were identified based on the presence of residues on surfaces with guano beneath them, and were swabbed for trace DNA. This method was then challenged against genetic analysis of guano and tissues present at the sample location to determine accuracy of the technique. This new technique has the potential to improve the ability to identify which species of bats have recently utilized roost, even when no animals are present, which will improve our ability to protect bats when roost sites must be disturbed. Further, it is cost effective and low risk to both animals and biologists. We encourage environmental professionals to consider utilizing this technique and contributing to evaluating its utility for various bat species in different habitat types.