The Coat That Closes the Circuit

The moment of contact

By the time an attack is happening, it is already at arm's length.

Most of the things sold for self-defence have to be found, pulled out and pointed. A spray is at the bottom of a bag. A stun gun is in a pocket. In the second it takes to reach for them, the other person has closed the distance, and often has hold of you.

I have wanted, for a long time, something that is already in place at that moment. Something you wear, not something you carry. Something that answers the exact situation a grab creates: two people, close together, with hands on each other.

So consider a jacket that is inert, ordinary and unremarkable, until both of your arms are on someone who is attacking you. Then it closes a circuit through them.

The idea

One contact at each wrist, and nothing else.

• A contact on each arm. A conductive band is woven into the outside of each sleeve cuff, made to look like ordinary trim. Clip-on gloves can move the contact out to the palms.
• The gesture is the trigger. Current flows only through whatever bridges the two contacts. One hand on someone does nothing. Brushing past a wall does nothing.
• The gesture is also the safety. The circuit is the space between your two arms, so it can only reach what you have taken hold of with both.
• Armed on purpose. Even then, it does nothing until you have armed it with a deliberate movement. Clapping, a handshake, or both hands on a railing are not enough.

Most stun devices put both electrodes a few centimetres apart on one tip. This one puts them as far apart as your two arms. That one difference is the whole idea, and, as it turns out, the whole problem.

Not a battery you wear

My first picture of this was the jacket itself as the store of energy: two conductive layers running through the whole garment, with the cloth between them, forming one large capacitor.

It would work, in a sense. The numbers are not absurd. A jacket’s worth of fabric, two layers a millimetre apart, holds about as much energy as one pulse from a stun gun. But it fails in every way that matters.

• You would be wearing a charged plate. Sweat, rain, a tear in the lining or a cut from a knife could discharge it into you instead.
• It is one snap, not a stun. Stun devices work by a train of pulses over a few seconds. A single discharge hurts, and then it is over.
• It is always live. It would have to sit charged all day, in case.

So the idea turned inside out. The jacket is not the battery. Its job is the opposite: to keep the wearer out of the circuit. A slim pack makes pulses only when the jacket is armed, and the cloth is insulation, wiring and two contacts.

The spread is the point, and the problem

Current takes the path between its two electrodes. What it does depends on what is on that path.

• Electrodes close together. A stun gun pressed against someone sends current through a few centimetres of skin. It hurts badly, but a determined, drunk or drugged person can push through pain.
• Electrodes far apart. Current that crosses a large part of the body makes large muscles contract whether the person wants them to or not. That is what actually stops someone. It is why TASER fires two darts that land well apart.

Two arms held apart give the jacket that spread without darts. It is what would make it work where a contact stun gun does not.

It is also the only arrangement in which the heart can be on the path. Hands on either side of someone’s chest send current across it. The risk depends on the path, on the charge in each pulse, on how long the pulses go on, on who is receiving them, and on bad luck in the timing of a heartbeat.

Effectiveness and danger here are not two dials. They are one dial. In this design, the one who turns it is the wearer, during a fight, frightened.

Four layers between the wearer and the worst case

The tension cannot be removed. It can be narrowed. Each of these covers another’s weakness.

• An energy cap, as the floor. Each pulse and each cycle is limited so that even the worst path, straight across a chest, stays within limits accepted as survivable for most people. Everything else sits on top of this. It also costs less than it seems: the wide spread still spends that capped energy across large muscles, which a capped stun gun cannot do.
• A trained gesture, as the default. The jacket comes with a taught movement: both hands on the other person’s upper arms, the way you would brace someone. It is a natural defensive motion, and it keeps the path through the shoulders, not the chest.
• A short warning, then the full cycle. The first contact gives a sharp warning pulse, a fraction of a second long. Only contact that continues gets the full cycle, and the cycle stops itself after a few seconds. The warning is short so that it is not a window in which to grab your wrists.
• Spread sensing, as advice only. Motion sensors in the sleeves estimate how far apart your arms are. When the spread looks chest-wide, the jacket lowers the dose. It never refuses to fire. A weapon that will not work when you need it is a danger of its own.

Off, armed, firing

The jacket has three states, and moving between them always takes something deliberate.

• Off. The pack is powered down. This is how the jacket spends almost all of its life.
• Armed. You cross your wrists and press them together, a nervous gesture people make anyway. The jacket ticks once against your wrist, a vibration only you can feel. If nothing happens within about a minute, it goes back to Off on its own.
• Firing. Both contacts on another person, while armed: the warning pulse, the full cycle, a hard stop and a cooldown.

Crossing the wrists needs both arms, so it rarely happens by accident. And it shows nothing. To anyone watching, you look scared, not armed.

Cuffs first, gloves when it is cold

The obvious place for the contacts is the palms, and my first sketches had gloves. But in summer, or in a warm city, gloves are the tell. Nobody wears them in the heat, and anyone who knows the jacket exists would know what to look for.

• The cuff is the base. A band of conductive fabric wraps the outside of each sleeve cuff, just above the wrist, with the insulation beneath it. When you grip someone’s arms, your wrists press against them naturally. The jacket works without anything else.
• Gloves are an upgrade. In winter, or on a scooter or a bike, matching gloves clip onto connectors at the cuff and move the contact out to the palms, which is easier to land.
• Broad, not pointed. The contacts are wide bands and patches, not studs, woven into the fabric so that they look like grip texture.

Hidden in a jacket

I want it to look like an ordinary technical jacket. Part of its value is that an attacker does not know it is there.

• Nothing shows. No light, no sound, no visible electrodes. The arming tick is felt, not heard.
• The pack lies flat. A slim, curved module across the lower back, shaped like a jacket’s back panel, removable for charging. It is the only rigid part.
• The warning pulse is the only warning. Because the jacket gives no visible sign, that first short pulse is the attacker’s one chance to let go before the full cycle. That makes it matter more, not less.

Concealment has a cost. In many places, a weapon disguised as something else is treated more harshly than one carried openly, and stun devices of any kind are restricted or banned in many countries, Australia among them. The better the jacket hides, the riskier it is to wear. This folio is about the idea; anyone who goes further needs to start with the law.

Never against the wearer

A weapon you wear is only as good as its ability to never hurt you.

• Insulation that assumes it is wet. Sweat, rain and blood are the normal case in a fight, not the edge case. The lining has to keep the wearer out of the circuit when soaked.
• It watches for leaks. If any current takes a path other than out of one contact and into the other, through the wearer, the jacket stops at once.
• It knows it is being worn. A skin sensor inside each cuff. A jacket on a hanger, or on somebody else, cannot be armed.
• Torn off, it goes dead. If a sleeve is ripped or a glove pulled away, the break in its wiring makes the jacket inert.

A sketch of the numbers

Rough figures, to show the scale. They are for the idea, not for building it.

Quantity	Value
Fabric area in a jacket	≈ 1.5 m²
Capacitance of two layers 1 mm apart	≈ 40 nF
Energy stored in it at ≈ 10 kV	≈ 2 J
Pulses in that store	one
Full cycle, then a hard stop	≈ 5 seconds
Warning before the full cycle	a fraction of a second
Time it stays armed with no contact	≈ 30–60 seconds
Spacing of the contacts, wrist to wrist, gripping someone	≈ 30–60 cm
Spacing of a contact stun gun’s electrodes	≈ 3–5 cm
Heart risk for this spread, with a cap	not yet known
Weight of the pack	not yet known

The number that matters most is not in the table. It is how low the cap can go and still stop someone, given the spread. That is the first thing I would want to learn, and it can only be learned carefully, by people qualified to do it.

The hard parts

Your arms are the first thing grabbed. Someone who pins your wrists has disarmed you. Putting the weapon on the arms puts it exactly where an attacker reaches first.

The wrong person in the circuit. In a real fight, the person between your arms is not always the attacker. A friend pulling you away, a bystander, someone frail. The warning pulse and the cap are there for them, but they do not make it harmless.

It cannot be made harmless. The cap can make the worst case survivable for most people. Most is not all. This is a less-lethal device, not a non-lethal one, and the folio should not pretend otherwise.

Wet, worn and washed. The insulation has to survive sweat, rain, years of wear and the washing machine, and fail safe when it does not.

Arming by mistake. People cross their arms and wrists all the time. The gesture has to be distinct enough not to arm on a cold tram, and easy enough to do while frightened.

The law. Restricted almost everywhere, banned in many places, and concealment makes it worse. This may be the hardest part of all.

Being turned around. If an attacker takes the jacket, it must be useless to them. The skin sensor helps; a pairing with the wearer, a ring or a watch, may be needed.

Where I would start

• On paper first. The questions are medical and legal before they are electrical: what cap is survivable across a chest, what stops someone, and where any of this could be legal at all.
• A jacket that only senses. A prototype with no energy in it: the cuff contacts, the wrist-cross gesture, the arming tick, the skin and spread sensors. Worn for weeks, it would show how often the gesture arms by mistake and how reliably the contacts land.
• Only then, a test rig. Any energised testing on a measured load, never on a person, and under the supervision of people qualified to do it.

Others who have tried parts of this

• Stun gloves are already sold to police and security staff, with contacts across the knuckles or palm.
• SHE, an anti-assault garment built in 2013 by engineering students in Chennai, discharged when the wearer was grabbed.
• TASER devices depend on wide spread between their two darts, which is what separates stopping someone from only hurting them.
• Contact stun guns are the close-electrode version, and the clearest evidence of why the spread matters.

What I add is the circuit between two arms: a gesture that is at once the trigger and the safety, hidden in a jacket that works without gloves, with layers that narrow the danger rather than deny it.

It can make the worst case survivable. It cannot make it harmless. And in the moment, the wearer still chooses where it lands.