The objective of this study was to determine the ability of a passive temperature monitoring system consisting of radio frequency identification (RFID) boluses with thermistors and receiver panels to detect ovulation in high performing dairy cows. The twice-daily reticulo-rumen temperature (Trr) acquisitions of 41 early-lactation Holstein dairy cows were analyzed. The data were analyzed using two criteria: six baseline days (2d, 3d, 4d, 5d, 6d, 7d) and four temperature deviations (0.2°C, 0.3°C, 0.4°C, 0.5°C). The best criteria were chosen by selecting the baseline/deviation combination that gave the best positive predictive value (PPV). The system detected 93 true positive and 267 false positive alerts of ovulation, with a monitoring rate (MR) of 47% and a PPV of 46.2%. There were indications that the Cow Temperature Monitoring System could have a future as an ovulation detection aid, but due to the unreliability of the Wi-Fi transmission of acquisitions, more research needs to be conducted before definite conclusions can be drawn.