It's an unimaginable accident in many cases, but more than dozen children have already died in hot cars across the country this year; one just a couple months ago in Texas.
In just a few minutes, temperatures can rise by more than 100 degrees.
It's an all too common sight. This summer, more than a dozen kids, nationwide, have died after being left inside hot cars.
San Angelo Fire Department Assistant Chief of Operations, Scott Farris, says it's a matter of minutes before a life can be in danger.
"It takes extra seconds to unbuckle a kid and take them with you versus I'm going to save some time and run in and out right quick. That time might be all the time it takes for your kid to get sick," Farris said.
With temperatures nearly 90 degrees outside, in an air-conditioned vehicle temperatures are at a cool 60 degrees. After only five minutes the temperature in a closed standing vehicle can increase by a sweltering 100 degrees.
Farris says, children and even pets are at a much greater risk of heatstroke.
"You don't realize what they're feeling, and a lot of kids can't tell you. You know all they can do is cry or you know fuss a little bit, but their body core starts getting up and it starts affecting their system; they start getting a fast heart rate, they start breathing fast, they'll start sweating," Farris said.
Since 1998 more than 720 kids have died after being left in hot vehicles, an average of 38 each year.
It's common for people to get distracted, but there are ways to prevent this tragedy.
"Put your purse back there with the kid or your brief case or whatever it is you're carrying. Wherever you're going that way you can think 'oh i got to get that' it might help you remember that your kid is back there also," Farris said.
San Angelo Animal Services Manager, Julie Vrana, says if it's too hot to be outside with your child the same pertains to your pet.
"Let them in to enjoy the cool with you. You don't want to be outside, so they don't want to be outside either," Vrana said.
Side-effects may not always seem evident. Hydration is key.
"They're not going to be very responsive, the eyes kinda start to roll, they have that glazed over look in their eye and they'll be laying on their side pretty much," Vrana said.
Farris says, if you witness a child or pet abandoned in a hot vehicle call 9-1-1 immediately.
"You know busting a window out that's what we'll do to get to a kid," Farris said.