To enable Product Alerts, go to Settings > Emails in the left menu and scroll down to Product Emails. Here you will see an email for Product Price Alert and Product Stock Alert. Enabling the email will enable the feature.
Product Price Alert should always show up but to see Product Stock Alert you'll need a product that is out of stock.
Once a customer has subscribed you will be able to see a list of the customers on the Product Edit screen under the Product Alerts tab.
A customer will be able to login to their Account and see a list of the Alerts they have subscribed to.
These links are provided in the Theme Editor.
You are able to open up the My Account page in your Theme and edit the Account Links to add or translate the link text.
Updated about a month ago