Abstract: With increasing interest in natural interaction (such as gesture or body motion), researchers are exploring sensors and algorithms that more accurately detect these user interactions unobtrusively to create opportunities for new applications. The HeatWave system describes our exploration of digital thermal imaging cameras to detect, track, and support user interaction on arbitrary surfaces. Thermal sensing has had limited examination in the HCI research community and is generally under-explored outside of law enforcement and energy auditing applications. This paper describes HCI applications for this technology, our algorithm implementation, and highlights how this new imaging technology might complement or augment more traditional RGB (video) and/or depth cameras. We identify unique contributions and opportunities afforded by thermal imaging and its limitations as a practical sensor for naturalistic user interaction.