The sensor implanted in the genitals of Fiona or Bella (favorite names for Swiss cows) measures body heat, then transmits the result to a sensor affixed to the cow’s neck that measures body motion. (Cows in heat become restless.) “The results are combined, using algorithms, and if the cow is in heat an SMS is sent to the farmer,” said Claude Brielmann, a computer specialist who helped design the system. The detector on the cow’s neck is equipped with a SIM card so the farmer can pay for the calls.

“Our recognition rate is about 90 percent,” Mr. Brielmann said.

The device, known as a heat detector, raises concerns among animal rights advocates, not so much because of its intrusiveness in the private parts of the cow — its use involves inserting a thermometer with a tiny transmitter and antenna in the cow’s genitals — but because of what it says about the stressful lives of Swiss cows. It also prompts skepticism among dairy farmers, who are startled by its cost, which is expected to be at least $1,400 per unit.

“Will it bring anything financially?” asked Ulrich Tschanz, 76, who raised Red Holsteins in the neighboring town of Oberlindach, where the clanking of cow bells is everywhere, until he turned over his herd of 40 cows to his son some years ago. “Always keep an eye on your cows, keep an eye on them,” he added. “That’s the best.”

But experts say measures taken to increase milk production — adding proteins, minerals and vitamins to their feed— upset the cows’ metabolism, making the device increasingly necessary. “With greater productivity there is a drop in reproductive activity,” said Samuel Kohler, a veterinarian who is among the developers of the device and now serves on the board of the company, called Anemon, that hopes to sell it. “It happens fairly frequently that you miss the right moment.”