Lt. Jason Short believed he was about to save a life.

A 911 call — someone had spotted a baby left alone in a car on a hot July day — prompted the police officer to rush to the Walmart shopping plaza in Keene, N.H. There, just as the call had said, he spied an infant in a car: a blanket, a bottle and finally two bare feet, motionless, emerging from beneath the fabric.

He drew his baton, smashed the window and saved the child.

Something was wrong. He described the infant as appearing lifeless or dead. Short began administering CPR. It did not work. He called for an ambulance, and then he checked for an obstructed airway.

“And I went to put my finger in its mouth and it was all resistance,” he said to WMUR-TV. “And I’m like, ‘This is a doll.’” He called the ambulance again, to relay its services were no longer needed.

The doll, as it turned out, belonged to a Vermont resident named Carolynne Seif­fert. That the figure was so realistic was not a mistake. Seiffert, whose 20-year-old son died in 2005 from Hunter’s disease, collects lifelike dolls as a form of coping with the loss. She owns about 40 of them.

Such dolls are known as reborn dolls, mimics of human babies in exquisite artificial detail. Many start out as regular, $30-a-pop toys, although the end product can fetch thousands of dollars. As the New York Times described in 2005, in the processes of “reborning” a doll the item is first dismantled, cleaned of paint and recolored, “often using a blue that helps the artist achieve a realistically veiny look. Glass eyes may be substituted for the original plastic ones. Hair is removed and replaced, sometimes with hand-implanted mohair or even human hair. ” To simulate the weight of a real infant, the doll’s body cavity may be filled with pellets.

There is little medical research into the value of reborn dolls for grief. But columnist and psychiatrist Gail Saltz wrote at Today in 2008 that dolls may act as transitional objects, items that help overcome a sense of abandonment. “For some women, such a transitional object eases them into ways of finding more external methods of dealing with their needs of caretaking and loving a being who loves them back,” Saltz wrote. “It is the concretized fantasy of getting unconditional love.”

Seiffert, who named the $2,000 doll Ainsley, sent a statement to WMUR, saying that “I’ve been laughed at and embarrassed by all the fuss,” and, “You can’t know how people choose to deal with their losses in life.”

The Keene police chief, Brian Costa, told the Union Leader he would pay the $300 to fix Seiffert’s window. He supported Lt. Short’s actions. “If all indications are that a baby is in a car in upward of well over 90-degree weather,” he said to the Union Leader, officers will break car windows. This is not the first time emergency responders have broken car windows to save what turned out to be dolls; police recommend that such items are left in car trunks so as to be completely out of view, or taken with their owners.

Being left alone in a parked car can be dangerous to young children. By the last week of July 2016, 21 children, many younger than 2, died of heat exposure after being left unattended in a car. The annual average is 37 deaths.

A car “is basically a greenhouse, and it’s a very effective greenhouse,” Jan Null, a meteorologist who has been recording child heat stroke deaths for more than a decade, told The Post in July. External temperatures of 86 degrees or higher may cause the car to heat to mid-150 degrees in under an hour, Null’s research found. Children left in cars have died when the temperature outside was in the 60s.

“I would never assume that it’s a doll,” Short said to WMUR. “I would always assume that it’s a child. I would never do anything different.”

Seiffert said she will affix a sign to her car, to warn other would-be rescuers to leave her windows unbroken as Ainsley is not real.