These systems are being revisited for the first time in a generation. Honest mistake is far more likely.
[0]https://static01.nyt.com/images/2018/01/14/us/14xp-hawaii-su...
[1]https://www.congress.gov/bill/109th-congress/house-bill/5785...
[2]http://www.abc.net.au/news/science/2017-12-03/after-25-years...
[3]https://isogg.org/wiki/How_long_is_a_generation%3F_Science_p...
Clearly there is a whole bunch of new attention being paid towards this.
And rightfully so given the provocations from NK and the general decline in maintenance/quality of the US nuclear and ICBM weapon systems.
In Denmark we have a national system of sirens. They are tested once a year at a specific date and time. In the cold war era they used to test them every Wednesday at noon, but it has been scaled down since then :-)
(This false alarm was a push alert sent to cell phones. What about people who don't have a cell phone on them when the alert comes? ... good luck)
They are primarily for tornadoes rather than nuclear weapons though.
At 5pm they play a 30-second traditional Japanese lullaby. If you ask people, they say it means it's time for children to go home - though as far as I can tell it has nothing to do with actual school schedules. I'm not sure everyone realizes it's actually a warning system.