Alerts for specific items on websites?

Mods I apologize if this is the wrong place so please delete if so.

Hi all. I’m not super tech savvy but I’ve been wondering lately about if there’s a way to have something monitor if a specific product goes on sale and be alerted. I searched and I only found something for Amazon.

The other thing I was wondering, I often use an auction website to buy items. Is there a program or app out there that would do something similar if a specific item/key word becomes available to automatically notified. As if it was checking the site automatically, daily?