Petrov Day is a tradition celebrating Soviet military officer Stanislav Petrov, who played a key role in preventing a nuclear attack during a false alarm incident on September 26, 1983.

How to celebrate [stub]

petrov.com has an organizer's guide for a small quiet ceremony, and Modes of Petrov Day contains additional ideas. Otherwise see the many posts tagged Petrov Day for things people have done in various times/places/groups.

LessWrong Website Celebrations

The LessWrong site has an annual tradition of commemorating the day involving users having the potential to take down the LessWrong frontpage for 24 hours. This has happened since 2019. Here are the relevant posts.

Year	Announcement	Retrospective
2019	Honoring Petrov Day on LessWrong, in 2019	Follow-Up to Petrov Day, 2019
2020	Honoring Petrov Day on LessWrong, in 2020	Postmortem to Petrov Day, 2020
2021	Petrov Day 2021: Mutually Assured Destruction?	Petrov Day Retrospective: 2021
2022	LW Petrov Day 2022 (Monday, 9/26)	Petrov Day Retrospective: 2022
2023	N/A	Petrov Day Retrospective, 2023 (re: the most important virtue of Petrov Day & unilaterally promoting it)
2024	[Completed] The 2024 Petrov Day Scenario	2024 Petrov Day Retrospective

See also

Existential Risk, Ritual