How to break a car window with a spark plug

Q: Can a spark plug break a window quietly?

Use a Sparkplug Its made to deliver electricity to your car engines combustion chamber, but it can be used for another purpose – breaking the glass. Believe it or not, this little fella is super-effective when it comes to breaking glass quietly! In fact, its much quieter than your safety hammer!

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Why do spark plugs break windows?

I’ve heard that spark plugs can instantly break car windows, which is handy in an emergency. I just don’t understand why they would be better than something like a hammer. Why is it that spark plugs break windows more effectively?

Car windows are made to be strong and withstand damage, but a spark plug can easily break through. Spark plugs break windows because they’re made from aluminum oxide ceramic (porcelain) and put a tremendous amount of energy at a single point on the glass.

So if you can throw a spark plug even moderately hard at a window, this should break it with ease. In addition to having one handy in case of an emergency, you may also want to put together an emergency kit in your car. You can also add either roadside assistance or towing and labor coverage to your insurance policy for added peace of mind.

Hopefully, you never have to use a spark plug to break your car window in an emergency. But you can give yourself some peace of mind by shopping for a cheap car insurance policy on the Jerry app.

Jerry is a licensed insurance broker that will collect quotes from over 50 top-rated insurers in minutes. After you find a great rate, Jerry can help you buy new insurance and cancel your old policy. Users save an average of $887 per year.

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If you're stuck in a sinking car, or outside your car and desperately need to get inside, you have plenty of ways to break that window, but one of the best might be right there in your car anyway—a simple sparkplug will do the trick with ease. This video from National Geographic shows you how it works.

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Whether you're inside your car and choose to keep a sparkplug handy just in case, or you're outside of your car and have access to one even if you can't get into your vehicle, Brian Brushwood explains in this video that if you break off a chunk of ceramic from around the sparkplug and use it against the car window safety glass, it'll shatter magnificently. The direct force on a small area applied by the sparkplug ceramic is enough to punch through the safety glass, which is designed to absorb great force over a large surface area without breaking (which is why a hammer, for example, doesn't work very well.)

I've seen people do this with the sparkplug ceramic, and others do it with the point of the sparkplug itself, but throwing the ceramic at the window is probably safer from the outside (since the glass is designed to shatter outwards if it breaks). We still think keeping a safety hammer and seatbelt cutter on your keychain or in your car is a better long-term idea, but this definitely works in a pinch—and remember, if you don't have either handy, you can always use your car headrest.

G/O Media may get a commission

Shattering the Shatterproof | National Geographic (YouTube) via Boing Boing

If you are stuck inside or outside your car, there are plenty of ways you can break the window. You can use a hammer, a knife, or any other material.

While all of these methods exist, one of the best ways is using a sparkplug. Sparkplugs are used in the car ignition; hence you can easily find them. They are also cheap, so if you can’t find one in your car, you can buy it from a nearby auto store.

Before you attempt using the spark plug, you should note that the plug works best in tempered glass commonly used in making the car windows. When the glass breaks, it shatters into many tiny pieces.

Another thing you should note is that you don’t need the entire sparkplug. While I have seen other people using the whole plug, you only need the spark plug insulator (the ceramic part).

I wouldn’t say breaking the car window with a plug is quiet. When done right, the spark plug shutters the glass immediately, and since the tempered glass is designed to break with little noise, not much noise is produced.

To break the glass with the spark plug, begin getting the plug either from inside or outside the car.

With the plug in hand, smash it into the ground or on the side of a masonry building. You can also use a hammer or metal bar. After smashing the plug, you should end up with porcelain chips with sharp edges. Pick one or two pieces and use them to break the glass.

You should be cautious when picking the pieces as they can cut your hand.

Toss the piece (s) at the window, and it will shatter. To have an easy time, target the centre or corners of the windowpane as they tend to shatter easily.

When done right, the sharp pieces should cause a tiny fracture in the tempered glass, which will instantly spread out. The window resembles a spider web of cracks, and you might even have an actual hole in the center.

As you can see in the video below, Mike tosses the ceramic piece, and the window shatters instantly.

Why does the spark plug work so well at breaking shattered glass?

The reason lies in its construction. During construction, the glass is cooled rapidly from liquid to solid. The glass that cools quickly ends up at a lower density; hence it has a higher volume than the glass that cools slowly.

Fundamental physics teaches us that there is a thermal gradient in a glass pane as it cools. This means that the outside of the glass cools much faster than the inside. This puts them outside of the glass in compression and the inside in tension.

These two forces serve as crack inhibition, where the stress necessary to propagate the crack has to overcome the compressive forces on the outside.

The result is a solid glass but has plenty of stored internal energy through the tempering process.

To break this glass, you need to use a small object that will serve as a stress concentrator. Since all the force you are applying to the window is coming from one tiny spot on the window, the window shatters fast.

The same glass that could handle the same type of pressure applied across its entire surface easily shatters when the same amount of pressure is condensed into one spot.

Let’s use an analogy.

Squeeze an egg barehanded (preferably over the sink). When you do this, you will be applying equal pressure all over the egg’s surface. For you to break the egg, you have to apply a lot of pressure.

Now try breaking the egg using a ring. The ring will concentrate the force you are applying, and in no time, you will wind up with goop in your hands.

Let’s use something else. You must have seen on magic shows magicians lying on a bed of nails. Why aren’t they hurt? This is because they evenly distribute their weight across all the nails and the force exerted to any nail isn’t high enough to break or even bruise the skin.

What would happen if the same magician stepped on a single nail? It would be an emergency case, right?

That is the same principle that works when you are breaking the window with a spark plug.

Do spark plugs work all the time?

This is an absolute no. The spark plug fragments won’t shutter the glass if they aren’t sharp enough, or you throw them with little force.

The porcelain shards are also ineffective on windshields as these windows come with a unique laminate feature that reinforces their resistance to impact.

What if you don’t have a spark plug, and it’s an emergency?

If you don’t have access to the spark plug, you can use any sharp porcelain shard. This can be broken:

Coffee mug
Smoking pipe
Ceramic ashtray
Dish from a nearby restaurant
Porcelain “china” keychain charm
Decorative item hanging from the rearview mirror
Item from a bystander, retailer, or nearby convenience store

When hitting the window, hit at its weakest point—usually near the center or at the ends.

Sparkplug chips can get you jailed.

In some states, broken shards of sparkplugs are considered a weapon. This is because they are used by burglars to break into vehicles. In California, for example, carrying sparkplug chips is regarded as a misdemeanor.

If caught carrying the chips, you risk a $1,000 fine or 6 months jail term.

Safety tips when using the spark plug

To avoid getting hurt, don’t throw the chip when you are too close to the window. This is because some glass might break off and hurt you. In some cases, the chip, might bounce off the window and get back at you.

If possible, wear safety glasses and work gloves before throwing the porcelain chip.

If there is someone in the car, ask them to stay away from the target window.

Final thoughts

Days are gone when you had to wait for a professional to help you break the window. With a simple spark plug, you can break the window without much fuss and save an emergency.

The spark plug works fast and easiest on the tampered glass, so you should use it on the rear windshield or car side window. Don’t try breaking the front windshield in an emergency as you will be looking like a dork, okay?

Will a spark plug break a window?

Car windows are made to be strong and withstand damage, but a spark plug can easily break through. Spark plugs break windows because they're made from aluminum oxide ceramic (porcelain) and put a tremendous amount of energy at a single point on the glass.

Can a spark plug break a window quietly?

Use a Sparkplug It's made to deliver electricity to your car engine's combustion chamber, but it can be used for another purpose – breaking the glass. Believe it or not, this little fella is super-effective when it comes to breaking glass quietly! In fact, it's much quieter than your safety hammer!