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How To Break A Window Silently With A Spark Plug

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.

How to break a window silently with a spark plug

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.

How To Break A Window Silently With A Spark Plug

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?


I hate noise with every single bone in my body and I'm here to share some of the tricks that have worked for me in my effort to keep off noises from noisy neighbors, noisy appliances, and so on. Buckle up for the ride.

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