What Counts as a Deadly Weapon in Arizona? ARS 13-105

Deadly Weapon vs Dangerous Instrument: What Does ARS 13-105 Actually Say?

Whether an object counts as a “deadly weapon” or a “dangerous instrument” is the hinge of Arizona assault law: it is the difference between a simple assault and a felony with mandatory prison. This is a short, definitional guide — the two statutory tests, real examples, who decides, and why the label matters less than most people expect.

If you are already charged, the definitions are only the starting point. Our deep dives on aggravated assault with a deadly weapon in Arizona and vehicles charged as weapons cover the charge itself — elements, penalties, and defenses — in full.

Both definitions live in ARS 13-105, the definitions section for Arizona’s entire criminal code, and they use two completely different tests:

• Deadly weapon — “anything designed for lethal use, including a firearm.” This is a design test: what the object was made for, not what happened with it. A firearm is a deadly weapon sitting in a glovebox — and the statute defines “firearm” to include loaded and unloaded guns, excluding only those in “permanently inoperable condition.”
• Dangerous instrument — “anything that under the circumstances in which it is used, attempted to be used or threatened to be used is readily capable of causing death or serious physical injury.” This is an as-used test: an ordinary object becomes a dangerous instrument only through proof of how it was actually wielded in this incident.

Two neighboring definitions give those tests their teeth. “Serious physical injury” means injury “that creates a reasonable risk of death, or that causes serious and permanent disfigurement, serious impairment of health or loss or protracted impairment of the function of any bodily organ or limb” — the high bar the dangerous-instrument showing must reach. And a “dangerous offense” is one “involving the discharge, use or threatening exhibition of a deadly weapon or dangerous instrument or the intentional or knowing infliction of serious physical injury on another person” — the enhancement that puts mandatory prison on the table under either label.

One wrinkle worth knowing: Arizona’s weapons chapter carries its own definitions in ARS 13-3101, including a nearly identical “deadly weapon” definition and the separate “prohibited weapon” category (automatic weapons, silencers, short-barreled shotguns, explosive devices). Those govern Arizona weapons and firearms charges like misconduct involving weapons — a different family of offenses from the assault designations this article covers.

How Do the Two Definitions Compare?

What Objects Do Arizona Prosecutors Actually Charge as Dangerous Instruments?

Because the definition says “anything,” the list is open-ended — and defense attorneys commonly see the same objects recur in Maricopa County charging documents:

• Vehicles. The most common dangerous instrument in Arizona. A car is never a deadly weapon — it is designed for transportation — but driven at or toward a person it is routinely alleged as one. Our guide to cars charged as weapons in aggravated assault cases covers that fight in depth.
• Knives and blades. These straddle the line. A dagger or combat knife can qualify as a deadly weapon by design; a pocketknife, box cutter, or kitchen knife is usually alleged under the as-used test instead. See our breakdown of when a knife is a deadly weapon in an Arizona aggravated assault case.
• Bats, clubs, and tools. Baseball bats, golf clubs, hammers, wrenches, tire irons — anything swung at a head is charged as readily capable of causing serious physical injury.
• Bottles and glassware. Bar-fight cases: a bottle swung or broken becomes a dangerous-instrument allegation almost automatically once stitches are involved.
• Footwear. Kicking someone on the ground gets charged with the boot or shoe alleged as the dangerous instrument — a fight that turns on the force used and the injuries produced.
• Unusual allegations. Because the statute says “anything,” prosecutors sometimes allege objects nobody thinks of as weapons — even a dog commanded to attack. The more unusual the object, the weaker the state’s “readily capable” proof tends to be.

Who Decides Whether Something Is a Dangerous Instrument — and How Does the Defense Fight It?

The jury does. Whether an object was a dangerous instrument as used is a question of fact, and the state must prove it beyond a reasonable doubt with evidence about this incident — not with the object’s reputation. That makes the designation one of the most attackable elements in an assault case, and the defense fights it on four fronts:

• How it was actually used. The as-used showing must be measured against real force, distance, direction, and duration — a bottle brandished across a room, a car rolling at parking-lot speed, or a single shove with a tool in hand often fails it.
• The injury bar. Serious physical injury means a reasonable risk of death, permanent disfigurement, or protracted impairment. Bruises, cuts, and soreness do not reach it — and when the actual injuries are minor, the “readily capable” claim invites hard cross-examination.
• Threatened use vs. mere presence. The definition requires the object to be used, attempted, or threatened. Holding a wrench during an argument is not the same as swinging one, and the line between possessing an object and threatening with it is where many designations collapse.
• Weapon function. On the deadly weapon side, the firearm definition excludes guns in permanently inoperable condition — operability and design are provable, testable facts, not assumptions.

The stakes fit in one paragraph: with the designation, an assault becomes aggravated assault under ARS 13-1204(A)(2) — a class 3 felony charged as a dangerous offense, meaning prison rather than probation on conviction. Without it, the same incident may be simple assault or a probation-eligible felony. The full sentencing ranges and (A)(2) defenses are in our guide to aggravated assault with a deadly weapon; the complete menu of aggravated assault theories is in our guide to ARS 13-1204 aggravated assault.

How Does Tamou Law Group Defend the Weapon Designation?

We treat the designation as its own case inside the case. In the first weeks we move to preserve the object itself before it is altered or released, secure video before retention windows lapse, and lock in the physical facts — distances, sight lines, injuries actually documented — while they can still be measured. Then we attack the as-used showing element by element: how the object was really handled, whether anyone was truly within its reach, and whether the injury evidence comes anywhere near Arizona’s serious-physical-injury bar.

The goal is leverage: when the dangerous designation becomes doubtful, a mandatory-prison case becomes a negotiable one. Our team includes former prosecutors, law enforcement officers, and public defenders who have argued both sides of these designations, as part of our broader Phoenix assault defense practice. Call 623-321-4699 for a confidential consultation about your specific situation.