GMA's Gio Benitez does hot car demonstration in Havertown, Pa.

HAVERTOWN, Pennsylvania (WPVI) -- Nationwide, Friday's big story is the heat. With heat indexes expected to top 100 degrees in the Philadelphia area, Good Morning America sent reporter Gio Benitez to Havertown to see just how high temperatures can go in a parked car.

"You'll be surprised at how fast the temperature in the car rises and how fast the body temperature rises," said Joseph Bushra, the Medical Director for Narberth Ambulance.

Benitez's live shot was set up at the back of the fire station, with paramedics on standby as he prepared to spend 45 minutes in a parked car with the windows up. It was an effort to demonstrate just how dangerous parked cars can be, particularly for children whose parents leave them in the car whether it's by accident or while the parent is running a quick errand.

Bushra says no parent should ever think an errand will be quick enough to leave a child in a parked car on a hot day.

"Because what happens is you get there and all of a sudden you realize you need seven other things that you didn't think you needed," he said. "And then and all of a sudden what you thought was a five minute trip is a 25 minute trip. And that can make all the difference."

Within 45 minutes, Benitez's body temperature rose to 101 degrees. He was sweating through his polo shirt and reported that he was having trouble thinking clearly. They are all reactions that first responders have seen before... and not just from children in hot cars. They also see people overheat in their own homes.

"We'll find people in houses with temperatures of 107, 108 degrees," said Bushra.

After he emerged from the car, Benitez featured a device in his live shot that could help prevent parents from forgetting that their children are in the back seat. The device, called Sense A Life, was developed by two fathers in Florida. It operates with a remote sensor that can be placed under a car seat. When the door is opened, the device speaks an alert to check for a child in the car.

"If we can save one life, we've all succeeded," said Sense a Life co-founder Fadi Shamma.

Bushra urges neighbors to check on one another and for parents and caregivers to not be in so much of a rush that they're tempted to leave children in the car.

"It's the worst mistake you can make. It's never worth it," said Bushra. "The few seconds you'll save, you'll regret forever."