Air Raid Siren https://www.amazon.com/Vixen-Horns-VXS-1450AR-Industrial-Alarm/dp/B010EEH13A/ref=sr_1_3?crid=1O2QBO5RW91KG&dchild=1&keywords=air+raid+sirens&qid=1589770016&sprefix=air+raid+%2Caps%2C151&sr=8-3
If he wants a hand crank one this works too. https://www.amazon.com/Vixen-Horns-Manual-Operated-VXS-1000SM/dp/B0106QZLCE/ref=sr_1_8?crid=1O2QBO5RW91KG&dchild=1&keywords=air+raid+sirens&qid=1589770178&sprefix=air+raid+%2Caps%2C151&sr=8-8