IPhone 7 made strange noise?

I was just holding my phone texting and whatever, sound off, and it made this really
high pitched beeping noise for 3 seconds, and it also vibrated while doing so. This has never happened before, and my phone is fairly new. Any idea what this is?

Amber Alert?

Hi so most phone shops have personnel who know what this mean. So time to consult with one.

Emergency alert. Did you not read the screen?