As of the launch of this question, it is generally believed that no fewer than nine countries in the world have nuclear weapons (Arms Control Association, Federation of American Scientists). For the purposes of this question, a "nuclear device" is one that is designed to produce a nuclear explosion utilizing the fission and/or fusion of nuclear fuel (e.g., Uranium-235, lithium deuteride). Whether a detonation is characterized as a test, an accident, a warning, or an attack is immaterial, and the detonation of a device in orbit around Earth will count. A radiological device (aka "dirty bomb") would not count (Nuclear Regulatory Commission). A device that produces an explosive detonation for a sub-critical test is not considered a "nuclear device" that is designed to produce a nuclear explosion (e.g., Arms Control Association). Whether or not a nuclear device has been detonated will be determined using credible, open-source media reporting. That determination must be made during the question's open period to count, as well as the detonation.

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