Ninja rocks - wikipedia Ninja rocks Ninja rocks are broken shards of spark plugs that are formed by smashing the ceramic portion of the spark plug with a hammer or other large object. Since they can quickly and quietly fracture the glass side windows on most cars, ninja rocks have been used in `` smash - and - grab '' auto burglaries since at least 1995. They have no traditional association with the ninja or ninjutsu, only being named such due to their `` silent but deadly '' function in burglaries. Contents 1 How they work 2 Legal status 2.1 United States Of America 2.1. 1 California 2.1. 2 Washington ( state ) 3 References How they work Tempered glass, which is used for the side windows of most vehicles, is manufactured with an extremely high surface compressive stress and high internal tensile stress, giving it strength and durability, but also leading it to abruptly shatter into thousands of tiny pieces when it breaks. When thrown with moderate speed at a side - window, a sharp shard of the exceptionally hard aluminium oxide ceramic used in spark plugs focuses the impact energy into a small enough area without blunting to initiate cracking, releasing the internal energy and shattering the glass. However, ninja rocks are ineffective if the shards are insufficiently sharp, thrown with too little energy, or thrown against windshields, as these are made of a laminated type of safety glass, and therefore do not shatter. Legal status The examples and perspective in this section may not represent a worldwide view of the subject. You may improve this article, discuss the issue on the talk page, or create a new article, as appropriate. ( April 2010 ) United states of america California In California, since 2003, ninja rocks are explicitly listed as burglary tools, and their possession with intent to burglarize is a misdemeanor punishable by up to six months in county jail and / or a fine of up to $1000. Legal records do not use the phrase `` ninja rocks '', preferring more precise phrases such as `` ceramic or porcelain spark plug chips or pieces ''. Until 2003, `` burglary tools '' in California did not include devices to break glass. In late 2001, two important convictions including possession of ninja rocks were appealed. In People v. Gordon ( 2001 ) 90 Cal. App. 4th 1409 ( Review denied ), Division 1 ( San Diego ) 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 rule of construction, 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 ) 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. 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 ( state ) One Washington trial court found that the ability of ninja rocks to quietly break tempered glass meant that their possession could be used to establish intent 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 Jump up ^ Ashton, David F. ( November 30, 2005 ). `` Valuables in car ? Thieves are `` smashing and grabbing '' ``. East County News. ^ Jump up to : Bridgewater, Carroll C. ( 1999 ). `` State of Washington v. Andrew Mcmanus : Opinion Information Sheet ''. FindLaw. Retrieved 2006 - 07 - 30. Jump up ^ ( The Dark Side of Tinkering by Edward Tenner 2001 US News and World Report Dec 24 2001, reprinted in 2003 Knowledge, Technology, & Policy vol 16 ( 2 ) 42 - 44 ) Jump up ^ McNamara, Danielle ( November 28, 2005 ). `` Officers fight auto theft with stepped - up patrols ''. Contra Costa Times. Jump up ^ Sonoma Police Department ( April 2006 ). `` Police Blotter ''. Sonoma Valley Sun. Archived from the original on 2006 - 06 - 02. Retrieved 2006 - 07 - 30. Jump up ^ Tenner, Edward ( 2001 - 12 - 24 ). `` The Dark Side Of Tinkering ''. U.S. News & World Report. Retrieved 2006 - 07 - 30. Jump up ^ National Geographic demonstration video Jump up ^ `` Documents associated with AB 2015 in the Session ''. California State Legislature. Retrieved 20 June 2016. Legal Judicial Council of California ( 2002 ). `` 2002 Legislative Summary '' ( PDF ). Retrieved December 20, 2005. See also Assembly and Senate committee analyses of AB 2015, among other records. Amended version of section 466 on FindLaw San Diego Legal Updates : Burglary Tools Retrieved from `` https://en.wikipedia.org/w/index.php?title=Ninja_rocks&oldid=828180903 '' Categories : Car theft Ceramic materials Crime in California Hidden categories : Articles with limited geographic scope from April 2010 All articles with dead external links Articles with dead external links from March 2018 Articles with permanently dead external links Talk Contents About Wikipedia Français Edit links This page was last edited on 1 March 2018, at 00 : 57. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: what part of a spark plug breaks glass
Answer: the ceramic portion