Ninja rocks is a colloquial term for an improvised weapon or tool consisting of the extremely sharp

porcelain Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

shards recovered from smashing or crushing the alumina insulator of a commercial spark plug. When thrown, ninja rocks are known to exploit the tensile stress present in the side windows on most cars in order to instantly shatter them, providing a quick and quiet alternative to other window-smashing methods and making ninja rocks ideal for emergencies or " smash-and-grab"

auto Auto may refer to: * An automaton * An automobile * An autonomous car * An automatic transmission * An auto rickshaw * Short for automatic * Auto (art), a form of Portuguese dramatic play * ''Auto'' (film), 2007 Tamil comedy film * Auto (play), ...

burglaries, having been used in the latter function since at least 1995. They have no traditional association with the ''

ninja A or was a covert agent or mercenary in feudal Japan. The functions of a ninja included reconnaissance, espionage, infiltration, deception, ambush, bodyguarding and their fighting skills in martial arts, including ninjutsu.Kawakami, pp. 2 ...

'' or ''

ninjutsu , sometimes used interchangeably with the modern term , is the martial art strategy and tactics of unconventional warfare, guerrilla warfare and espionage purportedly practised by the ninja. ''Ninjutsu'' was a separate discipline in some trad ...

'', only being named such due to their "silent but deadly" function in burglaries and a superficial resemblance to the

shuriken A ''shuriken'' ( ja, 手裏剣; literally: "hidden hand blade") is a Japanese concealed weapon that was used as a hidden dagger or metsubushi to distract or misdirect. They are also known as throwing stars, or ninja stars, although they wer ...

stereotypically used as a throwing weapon by ninjas.

Functionality

Ninja rocks take advantage of the physical properties of tempered glass, disrupting surface compressive stress and causing the glass to shatter.

Tempered glass Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tensi ...

, which is used for the side windows of most vehicles, is manufactured with an extremely high surface compressive stress and high internal tensile stress. This gives it strength and durability against shocks and blunt impact. When the glass breaks (such as in a serious vehicular collision) the internal stresses present in the pane cause the entire pane to shatter into thousands of tiny pieces. This reduces the risk of laceration one might otherwise face when using 'normal' glass, and is an essential safety feature in vehicular design. It is these physical stresses designed into tempered glass which make it vulnerable to ninja rocks. Made of shards of aluminium oxide ceramic, ninja rocks are very hard, and very sharp. When thrown at tempered glass, the ninja rocks' sharp, hard point focuses impact energy into an incredibly small area without blunting. This disrupts the glass surface compressive stress at the point of impact, subsequently releasing the internal potential energy within the stressed pane, shattering the glass. To be effective, a ninja rock needs to be sufficiently sharp, impact the glass on that sharp point, and impact it with sufficient force. Thrown ninja rocks may often fail to shatter tempered glass if one of these conditions is not met. Ninja rocks are ineffective against

windshield The windshield (North American English) or windscreen (Commonwealth English) of an aircraft, car, bus, motorbike, truck, train, boat or streetcar is the front window, which provides visibility while protecting occupants from the elements. ...

s, as these are made of a laminated type of

safety glass Safety glass is glass with additional safety features that make it less likely to break, or less likely to pose a threat when broken. Common designs include toughened glass (also known as tempered glass), laminated glass, and wire mesh glass ...

, and designed not to shatter.

Legal status

United States of America

California

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

, since 2003, ninja rocks have been explicitly listed as burglary tools, and their possession with intent to burglarize is a misdemeanor punishable by up to six months in

county jail A prison, also known as a jail, gaol (dated, standard English, Australian, and historically in Canada), penitentiary (American English and Canadian English), detention center (or detention centre outside the US), correction center, correct ...

and/or a fine of up to $1000. Legal records do not use the phrase "ninja rocks", preferring more precise phrases such as "

or porcelain spark plug chips or pieces". Until 2003, "burglary tools" in California did not include devices to break

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...

. In late 2001, two important

conviction In law, a conviction is the verdict reached by a court of law finding a defendant guilty of a crime. The opposite of a conviction is an acquittal (that is, "not guilty"). In Scotland, there can also be a verdict of " not proven", which is cons ...

s including possession of ninja rocks were appealed. In ''People v. Gordon'' (2001) 90 Cal.App.4th 1409 (Review denied), Division 1 (

San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United State ...

) of the Fourth District Court of Appeal found that possession of ninja rocks was not punishable under section 466 of the penal code. That court applied the ''

ejusdem generis Statutory interpretation is the process by which courts interpret and apply legislation. Some amount of interpretation is often necessary when a case involves a statute. Sometimes the words of a statute have a plain and a straightforward mean ...

rule of construction Statutory interpretation is the process by which courts interpret and apply legislation. Some amount of interpretation is often necessary when a case involves a statute. Sometimes the words of a statute have a plain and a straightforward mean ...

, deciding that ninja rocks were not enough alike the then-listed burglary tools. On the other hand, in ''In re Robert B.'' (2001) 93 Cal.App.4th 963, Division 3 (

Orange County Orange County most commonly refers to: *Orange County, California, part of the Los Angeles metropolitan area Orange County may also refer to: U.S. counties *Orange County, Florida, containing Orlando *Orange County, Indiana *Orange County, New ...

) contradicted this interpretation of section 466 and upheld the conviction. On February 13, 2002, the latter case was granted review by the

California Supreme Court The Supreme Court of California is the highest and final court of appeals in the courts of the U.S. state of California. It is headquartered in San Francisco at the Earl Warren Building, but it regularly holds sessions in Los Angeles and Sac ...

. Two days later, the state assembly proposed in Assembly Bill 2015 to amend section 466 to include ninja rocks. The bill passed unanimously in both houses in August 2002.

Washington

One

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

trial court A trial court or court of first instance is a court having original jurisdiction, in which trials take place. Appeals from the decisions of trial courts are usually made by higher courts with the power of appellate review (appellate courts). Mos ...

found that the ability of ninja rocks to quietly break

tempered glass Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tensi ...

meant that their possession could be used to establish

intent Intentions are mental states in which the agent commits themselves to a course of action. Having the plan to visit the zoo tomorrow is an example of an intention. The action plan is the ''content'' of the intention while the commitment is the ''a ...

to commit burglary, even in a case where the ninja rocks were not actually thrown at any glass because the burglars had found an unlocked door. One defendant appealed his conviction to the Court of Appeals on the grounds that "the trial court erred by admitting an unusual burglary tool into evidence". The Court of Appeals denied this reasoning and upheld the conviction.

References

;Legal * **See als
Assembly
an

committee analyses of AB 2015, amon
other records

on FindLaw *San Dieg
Legal Updates: Burglary Tools
{{DEFAULTSORT:Ninja Rocks Motor vehicle theft Ceramic materials Crime in California