Heat stress in dairy cows negatively affects production and animal welfare. To improve early detection of heat stress, a real-time body-temperature detecting microchip was developed for subcutaneous insertion at the base of the ear of dairy cows. Although previous research has validated the accuracy of microchip temperature detection, little is known about how well cows tolerate this device. Our objective was to evaluate dairy cows’ behavioral reactions toward the microchip as potential indicators of negative effects on animal welfare. We predicted that, if the cows responded negatively to the microchip, there would be an increase in the frequency of the focal behaviors after the implant. This pilot study enrolled lactating Holstein cows (n = 3). The cows were video recorded for 90 – 100 min/d starting at 1330 h for 5 d:2 d before and 3 d after the microchip (2 mm × 12 mm) insertion. A single trained observer (blind to both the ear with the implant and the day relative to insertion) recorded the frequency of ear flicks, head rubs, and head shakes. The frequency of each behavior (in bouts/min) were calculated and averaged among the days before and after the microchip insertion for each cow, and differences between the implanted and control ears were calculated within the pre- and post-implant periods. Differences between the pre- and post-implant periods were evaluated using a Wilcoxon signed-rank test. No difference was detected between pre- and post-implantation for ear flicks (control ear before: 0.04 ± 0.01 bouts/min, after: 0.03 ± 0.02 bouts/min; implanted ear before: 0.03 ± 0.01 bouts/min, after: 0.23 ± 0.38 bouts/min; differences between ears: P = 0.18), head rubs (before: 0.01 ± 0.01 bouts/min, after: 0.02 ± 0.01 bouts/min; P = 0.79), and head shakes (before: 0.01 ± 0.01 bouts/min, after: 0.04 ± 0.03 bouts/min; P = 0.42). Our results suggest that, in this pilot study, the subcutaneous insertion of the biosensor had little observable adverse impact on the welfare of the dairy cows. Future research is planned with a larger sample size and longer behavioral observation periods to further evaluate how well cows tolerate the biosensor.