This is definitely a cautionary tale. Pennsylvania couple, Keith Payton and Salina Johnson, reportedly died while having sex in their parked car. Police believe that carbon monoxide poisoning caused the couple’s death, as they were parked in an enclosed garage with the car’s ignition still running, according to the Daily Mail.

Payton and Johnson, both 40, were found dead Friday night. Their car’s ignition was still on, but it had already run out of fuel by the time law enforcement arrived. According to The Patriot News, police speculated that the couple were engaged in sexual contact at the time of their death because Johnson was not fully clothed. High levels of carbon monoxide were detected in the garage. Marijuana and drug paraphernalia were also found in the car. The couple were pronounced dead at 10:45p.m., but police believe they died long before being found.

Carbon monoxide poisoning happens when a person is exposed to way too much of the colorless, odorless gas. Since it’s undetectable to human senses, carbon monoxide is particularly deadly. According to the Mayo Clinic, too much carbon monoxide can diminish one’s ability to absorb oxygen, leading to severe tissue damage and eventually death. The most common source of carbon monoxide in our everyday lives is car exhaust, especially in an unventilated space. Other appliances that may cause carbon monoxide poisoning include charcoal grills, water heaters, portable generators, fireplaces, and furnaces.

Just as carbon monoxide itself is hard to detect, so is carbon monoxide poisoning. Symptoms of poisoning include dizziness, vomiting, shortness of breath, confusion, and blurred vision. Unborn babies, young children, and elderly adults are at increased risk of dying from carbon monoxide poisoning.

Strangely enough, Payton and Johnson are not the first couple to succumb to carbon monoxide poisoning while engaging in sexual relations. According to the Daily Mail, Jorge Rodriguez and Melissa Pereira died of carbon monoxide poisoning last month while parked in a Pennsylvania garage with the engine of Rodriguez’s Honda Prelude still running. The couple was fully clothed, but had retreated to the area for a romantic anniversary getaway.

The lesson to take away from these tragic couples? If you’re going to have sex in your car, make sure that you either turn your engine off, or alternatively, make sure you are in a space that is well-ventilated to avoid carbon monoxide poisoning.