1
Turn the widget on
Go to Widgets, turn Price drop alert ON, and choose Customize.
2
Set the trigger and popup
Edit the trigger label and the popup the same way as Back in stock.
3
Publish
Choose Publish so the widget loads on the storefront.

The alert compares the new Shopify price to the price stored when the shopper subscribed. A compare-at or “on sale” badge alone does not send the email.