: SoundBible and Soundsnap provide categorized alert sounds, including emergency signals like the "Tornado Siren II," often available in both MP3 and WAV formats.

: While MP3 is the most common for notifications, ensure your device or software doesn't specifically require WAV or OGG formats.

: Most sites offer "Royalty-Free" sounds, but some may require "Attribution" (giving credit to the creator), especially for commercial projects.

: You can move your downloaded MP3 to the Notifications folder on your internal storage, then select it via Settings > Sound & vibration .