Can I Sleep in My Car With the Windows Rolled Up? Can I Suffocate?

If you ever find yourself in a situation where you have no choice but to sleep in your car, you need to know how to do so safely. Is it a good idea to sleep in the car with the windows rolled up?

You can sleep in a car with the windows rolled up while the engine is not running. You will not suffocate because cars are not airtight. Oxygen can still get inside. However, leaving the engine running while you sleep does put you at risk of carbon monoxide poisoning.

Read on for everything you need to know about sleeping in your car with the windows rolled up.

Sleeping in a car with the windows rolled up.

Can You Suffocate in a Car?

It is virtually impossible to suffocate in a car with the windows closed. An average-sized car can hold 3,000-4,000 liters of air. To put it into perspective, a study analyzing the rate of air exchange in stationary vehicles states that there would have to be nine or more people in a car for the oxygen level to drop low enough to be dangerous.

Depending on the size and model, the air in a car is replaced with fresh air every 1-3 hours. However, it’s important to note that the study did find that the air exchange rates per hour were higher for older cars than newer ones. 

Are Cars Airtight?

Cars are not airtight, so they will likely not cause suffocation. A vehicle’s components and structure enable some fresh oxygen to pass through its interiors.

If cars were airtight, you wouldn’t be able to close the doors easily because of the difference in pressure inside and outside the vehicle. Furthermore, if cars were airtight, they wouldn’t sink; they’d float, and if oxygen were not coming into a vehicle from outside, people driving with the windows closed would suffocate on long trips.

Cars have vents that allow air to come in from outside, and the seals around the doors and windows are not airtight. But it’s not just oxygen that seeps into a car; other emissions from your engine can get in, too.

Can I Roll the Windows Up With the Engine Running?

It’s not safe to roll windows up and leave the engine running if you intend to sleep in the car. There’s a high risk of carbon monoxide poisoning in this scenario. However, there are times when it might make sense to roll up the windows, especially if you’re not sleeping for long.

Ideally, you want to leave the car’s windows slightly open while you sleep if you are doing so with the engine running. However, if the outside temperature is too cold or too hot to sleep comfortably or if you are concerned about insects or criminal activity, you need to be aware of the risks that come with keeping your car’s windows closed.

Although all cars manufactured after 1975 have catalytic converters that lessen carbon monoxide emissions, carbon monoxide poisoning is still possible while sleeping in a car with the engine idling.

What Is Carbon Monoxide Poisoning?

Carbon monoxide poisoning occurs when carbon monoxide has replaced the oxygen in your red blood cells. Your vehicle releases carbon monoxide and, when too much is inhaled, it can be dangerous or even fatal.

Carbon monoxide (CO) is a colorless, tasteless, odorless gas. It is present in fumes from combustible engines. It is a by-product of burning fuel. It is extremely dangerous to inhale these fumes because they can replace the oxygen in red blood cells quickly.

At least 400 people die in America every year due to carbon monoxide poisoning. People who are intoxicated or sleeping can die before they even know that they have been poisoned. Because cars are not airtight and allow oxygen exchange, carbon monoxide from the exhaust can replace the oxygen in the passenger compartment.

What Are the Symptoms of Carbon Monoxide Poisoning?

If you have been exposed to carbon monoxide, you may experience flu-like symptoms, including:

  • Headaches
  • Muscle aches
  • Fatigue
  • Dizziness
  • Chest pains
  • Nausea
  • Vomiting
  • Chills
  • Brain fog

Ultimately, the severity of carbon monoxide poisoning depends on how long you are exposed to it. However, even small amounts of carbon monoxide can cause long-term neurological issues, incapacitation, and even death.

Minimize Health Risks By Turning Off the Engine

To sleep in your car safely, eliminate the risk of carbon monoxide poisoning. Turn off your engine, and do not leave it idling while you sleep. Although this is not ideal for climate control inside the car, there are other ways to make yourself more comfortable.

  • To stay cool – You can buy a small portable fan or a similar gadget that will keep you cool. It should be powerful enough to keep you cool for a few hours.
  • To stay warm – You can insulate your car. Lay your seats down flat and use towels and blankets for extra padding and warmth. I also recommend getting this TETON Sports Sleeping Bag. It is super comfy and will most definitely keep you warm.
  • Keep insects out – If you need to open your windows but want to keep bugs out, I recommend these EcoNour Car Window Screens for Camping that you can place over any open windows. You can also use insect repellants like Peaceful Sleep.  

Tips for Sleeping in Your Car With the AC On

If you find yourself in a situation where you need to sleep in your car with the A/C on because of extreme weather conditions, there are ways to minimize the risk of carbon monoxide poisoning.

Use the “Fresh” Air Setting

While having the car’s windows open is the best way to ensure fewer carbon monoxide emissions in the passenger compartment, the “new” or “fresh” air setting on your air conditioning unit is the second best. The “recirculate” setting is proven to be less effective at minimizing the carbon monoxide emissions inside your car.

Park in an Open Space

Do not sleep in your car with the engine running (windows open or closed) while you’re in a garage or any other poorly ventilated space.

Carbon monoxide will get into the car quicker in a poorly ventilated space. In open spaces, there’s more room for diffusion.

Carry Out Proper Maintenance

Always give your car a once-over or get it seen by a mechanic before you sleep in it to make sure the exhaust system and A/C system are working correctly.

Your mechanic should also make sure that your car does not have any leaks in the exhaust system – this includes the tailpipe. A leak in the exhaust system is caused by rust, age, accident damage, or blockage.

Check for any holes in the body panel, such as the trunk, firewall, or floorboard. These gaps can also allow the carbon monoxide from your car to enter the passenger compartment.

Check the Area Around Your Car

Inspect the area around where you’ve chosen to park your car. Clear away any snow, water, or mud that could get into the tailpipe and block the exhaust.

Don’t park near other cars that are idling – you don’t want other cars’ emissions seeping into your vehicle.

Buy a Carbon Monoxide Detector

You can buy a small CO detector for absolute peace of mind that you can place in your car. The device will emit a loud warning beep if it detects any CO in your car, so put it inside the car where you will hear it.

Other Dangers of Sleeping in Your Car

While carbon monoxide poisoning is the most dangerous factor to consider when sleeping in a car with the engine running, there are other things that you should be aware of. The outside temperature and intruders – human and animal – also pose a risk.

Extreme Temperatures


According to studies, the inside temperature of a car after one hour is around 40 °F (4.4 °C) hotter than it is outside.

Although determining exactly how hot it will get inside your car depends on many external factors, it’s safe to say that the temperature inside your car can escalate quickly – and cracking a window won’t help. 

While infants and pets are more susceptible to dehydration and heatstroke because they cannot communicate their discomfort or take corrective action, it’s crucial to consider sleeping somewhere other than in your car if it is sweltering outside. 


At the other extreme, you are at risk of hypothermia and frostbite if the outside temperature is lower than 40 °F (4.4 °C) – especially if the interior of your car is damp.

When there is a significant difference between the temperature inside and outside your car, condensation will occur. These droplets of moisture can accumulate on your clothes and make you feel even colder.

The solution to the dampness caused by condensation is to crack the windows. Always make sure that you dress appropriately and have enough insulation to keep yourself warm if you are sleeping in your car. 


If you are sleeping in your car, you may appear to be a soft target for criminals. Always keep your valuables out of view, only open the windows halfway to prevent anyone from getting in, and keep the doors locked.

Be aware of animals, especially bears. Bears can break into cars if they smell food, so keep your food in a bear-proof container or hanging in a tree outside if you are in bear country.

General Safety Tips

  • Don’t isolate yourself. If you are going to sleep in your car, make sure that you park in a well-lit area close to other people.
  • Check if it’s legal. Always make sure that you park in a place where it is legal to do so. You can safely park at rest stops, campsites, and most 24-hour Walmart parking lots.
  • Avoid parking on asphalt. If it’s hot outside – asphalt absorbs heat and can make the interior of your car hotter. If you can, park somewhere shady.

Key Takeaways

There is no chance of suffocation due to insufficient air exchange while sleeping in your car with the windows closed; however, there is a small risk of carbon monoxide poisoning.

To eliminate this risk, the best thing to do is to turn the engine off while sleeping. If this is not possible, the above guidelines will ensure that a minimal amount of CO seeps into your car. 




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