The dairy industry relies on heat coagulation tests (HCTs) to determine high-quality milk heat stability for typical thermal processes. For the HCT, an oil bath heats 1–2 ml of milk to 140 °C. The test lasts 20–30 min and finishes with visual confirmation of milk coagulation. This time for coagulation is recorded as the HCT time. While standard in the industry, this test is time-consuming and prone to operator-dependent bias. Thus, an automated alternative for measuring HCT time is desirable. This work proposed the use of ultrasonic monitoring and employed 10 MHz contact and immersion ultrasonic transducers in combination with conventional pH and rheological sensors. Room-temperature skim milk was coagulated in standard containers with a Glucono-Delta-Lactone acid concentration of 3% while simultaneously being monitored by the ultrasound, rheological, and pH sensors, at testing rates of 1 s, ca. 6 s, and 2 min, respectively. The resulting ultrasonic wave speed measurements revealed an increasing trend throughout the coagulation process. Additionally, an inflection point within the increasing wave speed corresponded to rheological and pH parameters indicating coagulation. This work demonstrates the potential for ultrasonics to be used as sensors for coagulation within the dairy industry.