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Interdevice precision and accuracy are not investigated for precision livestock farming (PLF) technologies, but are fundamental for the use of data in populational metrics and to compare cows' data. This study aimed to validate a behavior monitoring collar (BMC; CowMed, Santa Maria, RS, Brazil) and its interdevice reliability. First, we compared observations with the BMC, and second the interdevice precision and accuracy for rumination, feeding activity, and idle time of lactating dairy cows. Holstein cows (n = 23) were housed in a voluntary milk system freestall barn and fitted with 2 devices within the same cow. Observations were made over 2 periods of one day (0700 to 1100 h, 1400 to 1700 h); the 7 h per cow were summarized for each behavior to assess the agreement of observed behavior and BMC data. To assess the interdevice reliability, 26 d of BMC data were summarized by day per cow for both devices. Pearson correlation (r), coefficient of determination (R2), Lin's concordance correlation coefficient (ρc), linear regression, and Bland-Altman plots (BAP) were calculated for each period of observation. For the validation, we found high correlations for feeding activity, very high for idle time, but low correlations for rumination. The BAP were deemed acceptable and without bias; BAP mean differences ± SD were 0.83 ± 4.01, −0.48 ± 4.15, and 7.17 ± 3.94 min/h for rumination, feeding activity, and idle time, respectively. The slope of the linear regression did not differ from 1 for any behaviors but idle. For interdevice comparison, we found moderate correlations for feeding activity and idle time, and a low correlation for rumination. The BAP was deemed acceptable and without bias; BAP mean differences were −0.36 ± 2.84, 0.45 ± 3.51, and −0.06 ± 2.81 min/h for rumination, feeding activity, and idle time, respectively. All slopes of the linear regressions differed from 1 except feeding time. Thus, the interdevice comparison did not meet the accuracy criteria. In summary, this study validated the precision of the BMC for recording feeding activity of lactating dairy cows.