We evaluated the accuracy and precision of zero-heat flux (ZHF) and dual sensor (DS) non-invasive temperature probes in intensive care unit (ICU) patients undergoing hypothermic temperature control, hypothesizing that both devices would accurately estimate core temperature. In a single-center prospective cohort study, we enrolled 35 ICU patients and applied continuous, non-invasive ZHF and/or DS probes to the lateral forehead or anterior chest to collect 358 observations. Conditions potentially influencing temperature estimation were recorded. Using Bland–Altman analysis with multiple paired observations per individual, we compared the bias between non-invasive probes and direct core temperature measurements. Lin’s concordance coefficient (LCC) was computed to quantify precision. The mean bias between the ZHF probe and invasive temperature was + 0.98 °C; for the DS probe, it was − 2.19 °C. In hypothermic patients, the ZHF probe’s accuracy improved (bias + 0.28 °C, LCC 0.86), while the DS probe remained inaccurate (bias − 2.52 °C, LCC 0.07). Clinical confounders like vasoactive agents or temperature control devices did not consistently affect bias, accuracy, or precision. Neither the ZHF nor DS non-invasive probes provided sufficient accuracy or precision to guide clinical decisions in the ICU. These results contrast with previous studies reporting biases within ± 0.5 °C. However, the ZHF probe showed promising limited deviation, especially in hypothermic patients.