This chapter describes the phenomenon of love tester machines: the first psychologically informed mechanisms designed and used to estimate the romantic compatibility between people. Love tester machines are amusement devices, often found in arcades, carnivals, and entertainment venues, designed to measure or simulate romantic affinity or “love potential.” Typically, these machines feature a scale that lights up or gives a reading when the user grips metal handles or places their fingers on buttons or sensors. The result is displayed in playful categories, such as “Hot Stuff” or “Cold Fish,” implying a level of romantic prowess or desirability. Though often marketed as reliable assessment tools, these devices work through basic principles like rotation motor, skin conductivity, temperature, or simply random algorithms and are intended purely for entertainment. Among the various technological artifacts that have explored human emotional makeup for effective matchmaking, love testers hold a unique place. They represent a fusion of technological advancement, entertainment, psychological inquiry, and the quest for understanding a romantic union. The history of those devices, their cultural significance, and technological evolution contribute new insight into the role of psychometrics, data, and algorithms in modern-day relationship culture, which this chapter overviews by tracing early twentieth-century love testers to their contemporary digital counterparts in broad contexts.