The device synchronises to a computer in the milk shed so electronically tagged cows can be drafted by the automated gate.
"Before, without a drafting gate, if you wanted to separate 10 cows one of the farmers had to stand outside the milking shed waiting for the cow," Mr Parmar said.
"He would have to check what number it was before scaring it into the paddock with hand motions or whatever.
"Farmers used to have to write down the number of the cow they wanted to draft, go to the computer and punch the number in.
"But now when the cow gets to the gate, it gets separated from the herd and the farmer doesn't have to do much.
"It's pretty clever."
Trials of the new drafter were done on four Waikato farms and one in the South Island.
Pop-up messages on the smartphone app tells a farmer when a cow has reached the gate, which can separate cows into three groups for greater efficiency.
The accuracy of the system has improved from about 78 per cent when Mr Parmar began trials, after software bugs causing problems with the automated gate were resolved.
It is now almost perfectly accurate at 99 per cent.
"It saves quite a bit of time," he said.
"In mating season when a farmer wants to separate 20 cows you had one person out there trying to scare the cows into a pen.
"But now both of you can just go in there and do the milking and get out of there a lot sooner."
