An air-raid siren sounds the warning

This year, we commemorate D-Day and the Normandy Landings. In remembrance, an Air Raid Siren will sound "The Warning" at 12:00pm, followed by the "All Clear" signal after the fireworks display around 22:10pm. 

For those interested in the siren's sound, the BBC offers a clip titled "Primary History KS2: WW2 Clips. An air-raid siren sounds the warning" on BBC Teach.