Is there a tool like this?

Hello bhw members, i'm looking for a tool that can notify me when a product will be on sale or under a preset price by me. Basically being able to notify me right away when products i selected will be on sale so i can resale them (that's the main purpose of course). I hope i described to understand what i'm looking for. Thanks.

On which platform do you want to sell the product? Amazon?

Keepa can do it. You can track the product price on amazon and get notification when the price drops.