Back-in-Stock Alerts: Keeping Shoppers Who Find It Sold Out
Short answer: Put a "notify me" form where the add-to-cart button would be on sold-out products and variants, collect an email (and a mobile number if you'll really use it), and send alerts automatically when stock returns. Neither Shopify nor WooCommerce does this out of the box: Shopify stores use a stock-alert app and WooCommerce stores use an extension such as Back In Stock Notifications. The underrated part is the data: the sign-up list tells you what to reorder, in which size, and how many.
Why it's worth doing
A shopper who lands on a sold-out product has already done the hard part: they found you and wanted something you sell. Without an alert, the only options are to leave or buy something they wanted less. With one, you keep a direct line to a person with a specific, stated want, and you learn about demand you'd otherwise never see, because a sold-out page records no sales.
Feature checklist for choosing a tool
Shopify's App Store lists hundreds of stock-alert apps (323 in the category as of November 2026), and WooCommerce has its own Back In Stock Notifications extension plus third-party options. Instead of comparing star ratings, work down this list.
Must have
- [ ] Works per variant, so someone waiting for a size 10 isn't emailed when size 8 arrives
- [ ] Appears on the product page automatically when stock hits zero and disappears when it returns
- [ ] Sends automatically on restock, with a manual option for staggered releases
- [ ] Lets guests sign up without an account
- [ ] Exports sign-ups (CSV at minimum), so the data isn't trapped in the tool
- [ ] Doesn't noticeably slow down product pages; check with a speed test before and after
Useful
- [ ] A minimum restock quantity, so restocking two units doesn't email 200 people
- [ ] Sends in batches or sign-up order (first come, first served)
- [ ] Reports: sign-ups per product and variant, emails sent, orders that followed
- [ ] Optional SMS or push, if you already text customers
- [ ] An opt-in box for marketing, kept separate from the alert itself
Nice to have
- [ ] Pre-order mode for products with a confirmed restock date
- [ ] Integration with your email platform for branded alerts
The WooCommerce extension covers several of these as documented: guests and logged-in customers can sign up, the form appears after the "Out of stock" status on simple products and variations, sign-ups can be filtered and exported to CSV, and you can set a minimum restock quantity before notifications go out.
Setup
Shopify
- Pick an app from the stock alerts category against the checklist above. Several list a free plan; check what the free tier caps, such as alerts per month.
- Install it and turn on its theme app block or embed in Online Store > Themes > Customise. Check sold-out products and sold-out variants on both mobile and desktop.
- Edit the alert email: product image, variant, price, a direct link to that variant, and a plain line saying stock is limited.
- Place a test sign-up, set the product's inventory to zero and back up, and confirm the alert arrives.
WooCommerce
- Install Back In Stock Notifications (or an alternative).
- Important: the extension's documentation warns that if you hide out-of-stock items from the catalogue, customers can't sign up. Under WooCommerce > Settings > Products > Inventory, make sure "Hide out of stock items from the catalog" is off.
- Set the minimum restock threshold and edit the email.
- Check your sending setup. The documentation notes that most email providers cap daily sends, and suggests a dedicated SMTP or transactional email service if you send in volume. A big restock sent through a basic host mailbox may simply not arrive.
Where the form goes
Replace the disabled "Sold out" button with the form, right where the shopper's eye already is. Keep it to one field and one button: "Email us when it's back". Say what happens next: one email when it's back, no newsletter unless they tick the box.
Sending order and fairness
If 150 people want 40 units, the alert becomes a race. Two fair approaches:
- First come, first served: alert in sign-up order, in batches roughly matching stock, with a pause between batches. Some tools do this; with others you can set a minimum quantity and release stock in stages.
- Everyone at once, with honesty: alert everyone and say plainly how many came in.
Whichever you pick, don't send alerts at 2 a.m. New Zealand time because the stock sync ran overnight. Schedule restocks so alerts go out at a sensible hour.
When a pre-order is better
If you have a firm date and you're confident in the supplier, taking pre-orders captures the sale now instead of a promise of interest. If the date is uncertain, stick with alerts; a pre-order that slips by weeks costs more goodwill than a waitlist.
Using the demand data
This is where alerts pay for themselves twice. Export sign-ups monthly and look at:
| Question | What to look at |
|---|---|
| What should we reorder first? | Sign-ups per product, ranked |
| Which sizes or colours? | Sign-ups per variant, compared with what you usually order |
| How much? | Sign-ups ÷ the share of past alerts that turned into orders |
| Is it worth bringing back at all? | Sign-ups on discontinued lines |
| Did the alert work? | Orders within a week of the alert, per product |
That third row needs your own history. After a few restocks, you'll know roughly what fraction of people who sign up actually buy. Until then, treat sign-ups as a ranking, not a forecast.
Watch the variant data especially. If most sign-ups for a jumper are for one size, your size curve for the next order is probably wrong, and that's a cheaper fix than a sale at the end of the season.
FAQ
Should I hide sold-out products instead?
Not if you want alerts: hidden products can't collect sign-ups. Keep them visible with a clear sold-out state unless the line is gone for good.
Can I text customers instead of emailing?
Some apps offer SMS. Only use it for people who gave a number for that purpose, and make sure you're comfortable with the cost per message.
How long should sign-ups be kept?
Set a limit, such as six months, and let people know. An alert for something they wanted last summer is more likely to annoy than convert.
Do alerts work for products that won't come back?
Not as alerts, but the sign-up count is still useful evidence when deciding whether to stock a similar product.
If you'd like back-in-stock sign-ups wired into your reorder planning, tell us how you track stock today.