This chapter shows that invasive measures of arousal such as functional magnetic resonance imaging, electroencephalography, skin conductance, and finger temperature have limitations that are less present in non-invasive measures such as thermal imaging and pupillometry. Invasive measures may induce arousal, thereby hindering the interpretation of results, and they may also remove the possibility of demonstrating a link between arousal and subsequent behavior. The chapter argues that thermal imaging and pupillometry are non-invasive measures of psychophysiological arousal. Thermal imaging and pupillometry, despite their potentially noninvasive capabilities to detect arousal, also share certain limitations with their more invasive counterparts. Thermal imaging, thermography, functional infrared imaging, or infrared thermography is a safe and increasingly affordable technique that records the radiation of energy released from the body. Thermal imaging might also be a good method to explore whether all moderating variables are equally strong in mitigating arousal.