The objectives were to quantify mounting behavior associated with estrus and to estimate the maximum heritability of this trait. Holstein-Friesian cows (n = 1,133) across 5 grazing herds located in the United States, New Zealand, and Ireland, were fitted with a FlashMate (Farmshed Labs Limited, Hamilton, New Zealand), a touch activated mounting detection device, to record the number of contacts and duration of the contacts received at estrus. FlashMates were removed after approximately 60d of breeding. Data were extracted from each device for individual cows. A peak detection program in SAS 9.4 (SAS Institute Inc., Cary, NC) was used to identify individual peaks and to calculate the sum of the contact time, in seconds, and the number of times contacted during estrus. Across all farms, there were 91 cows (8%) with no peak detected and presumed anestrus. The data from the remaining cows (n = 1042) with at least one peak (total of 1,758 peaks) were analyzed for the effects of farm and peak number by using PROC MIXED of SAS. There was an effect of farm on the duration of contacts (range of 37.8 ± 8.3 to 118.3 ± 2.2 s; P < 0.0001) and the number of contacts received (range of 16.9 ± 2.4 to 37.8 ± 0.6; P < 0.0001). The peak number (first and second) was not significant. The number of days between the first and the second estrus detected was affected by farm (range of 18.2 ± 2.1 to 25.1 ± 0.5 d; P < 0.001). The intraclass correlation coefficient (maximum heritability) was 21.1% for the number of contacts received and 18.7% for the duration of contacts. In conclusion, the number of contacts received, the duration of each contact, and the time between peaks differed between farms. The maximum heritability of the estrus traits measured was approximately 20%. Novel technology for estrus detection allows collection of estrus phenotypes in a large number of cows suitable for in-depth studies.