When a product sells out, the people who land on its page afterwards are some of the most interested visitors a store gets. They searched for it or followed a link, and found a button that says “Sold out”. Without a way to leave their details, most of them leave and do not come back.
A back-in-stock notification, also called a restock alert or waitlist, gives them a simple option: “Tell me when it’s available.” When stock returns, they get a message with a link straight to the product. Done well, it recovers sales and shows you which products people actually want. Done badly, it sends 300 people to a page with four units left.
Here is how to set them up well.
Key takeaways
- An alert is a promise. The customer asked for one message about one item. Keep it about that item.
- Placement matters more than design. The signup belongs where the add-to-cart button would be, on the variant the customer selected.
- Email suits most stores; SMS is faster but carries stricter consent rules.
- Small restocks need throttling. Alerting far more people than you have units creates a second disappointment.
- The signup list is demand data. Use it for purchasing decisions, not only for sending alerts.
How back-in-stock alerts work
The mechanics are similar whether the feature comes from your theme, an app, your email platform or custom code.
- A variant reaches zero sellable stock and the store shows it as sold out.
- The page shows a signup form in place of, or next to, the add-to-cart button.
- The customer enters an email address or phone number. The system stores it with the exact product and variant, the date and the consent wording they saw.
- The customer sees a confirmation, on screen and usually by email.
- Stock is updated. When inventory for that variant rises above zero, or above a threshold you set, the alert is triggered.
- Subscribers receive a message with the product, variant, photo and a direct link.
- The request is closed once the alert is sent, or kept open for one reminder if your settings allow it.
Automatic sending is convenient but needs the safeguards described below.
Depending on your platform and theme, alerts may be built in, or you may need an app or an integration with your email platform. Whatever you use, look for variant-level signups, a restock threshold, some form of batch sending, separate marketing consent, reporting by product and a way to export your data. Our checklist on how to choose Shopify apps applies to any tool that touches your storefront and customer data.
Where to place the signup
The best place is where the customer is already looking: the spot where the buy button normally sits.
- Product page, in place of the buy button. Replace “Add to cart” with a clear “Notify me when available” button or an inline field, and keep “Sold out” visible so nobody is confused.
- Tied to the selected variant. When someone picks size 10 and it is sold out, the form should say so: “Get an email when Size 10 is back.” If they switch to an available size, the add-to-cart button should return.
- Visible on mobile. Test on a phone. A form pushed below a long description is easy to miss.
- Not in a page-load pop-up. A button that opens a small form when tapped is fine; a pop-up asking for an email before the customer has chosen anything tends to be dismissed.
Keep the wording plain: “Notify me when available” or “Email me when it’s back”. Avoid “Reserve yours” unless you actually hold stock for people.
What to ask for
One contact field is enough. Name, birthday and preferences are not needed to send one alert, and each extra field reduces completions.
If you also want the person on your newsletter, add a separate checkbox, unticked by default, such as “Also send me news and offers.” The alert request is not consent to marketing, and treating it that way is the most common mistake in this area. Our guide to email and SMS consent basics explains the difference between a requested message and marketing.
Email or SMS?
| SMS | ||
|---|---|---|
| Speed | Read within hours for many people | Often read within minutes |
| Room for detail | Photo, price, variant, links | Short text and one link |
| Consent rules | Vary by country; generally lighter for a requested one-off message | Stricter in many countries, especially the US |
| Cost per message | Usually low | Usually higher; varies by country and provider |
| Customer tolerance | Fairly high | Lower; irrelevant texts feel intrusive |
| Best for | Most products and stores | Limited drops that sell out within hours |
Most small stores do well with email alone. SMS earns its place when restocks sell out fast and your customers have shown they want texts. If you offer both, let the customer choose one rather than collecting a phone number “just in case”. Our guide to SMS marketing for small stores looks at when texting is worth the cost and the extra consent work.
Consent and expectations
A customer who asks to be told when an item returns has asked for that message. That makes the alert easier to justify than a promotional email, but it does not make everything acceptable.
- Send what was requested: an alert about the item with a link to buy it. Heavy promotion of other products turns it into marketing, which may need separate consent.
- Say what will happen next to the form: “We’ll send one email when this item is back in stock.”
- Record the request: contact, product, variant, date, source page and the wording shown.
- For SMS, use wording that covers the alert texts specifically, identify your store in each message and honor stop requests. In the US, the TCPA and carrier requirements apply; elsewhere, check local rules.
- Expire old requests. If an item has not returned after several months, a message out of the blue may surprise people.
This is general information, not legal advice.
Timing and throttling when stock is limited
The hard part is not sending alerts. It is deciding what to do when 400 people are waiting and 30 units have arrived. Alert everyone at once and the first few dozen buy, while everyone else clicks through to “Sold out” again.
| Approach | How it works | Good for | Watch out for |
|---|---|---|---|
| Everyone at once | All subscribers alerted immediately | Restocks that comfortably exceed likely demand | Sell-out within minutes for small restocks |
| Waves, oldest signups first | Alert a batch, wait, check stock, alert the next | Limited stock and long waitlists | Choosing batch size and wait time |
| Restock threshold | Only send when stock reaches a minimum | Avoiding sends triggered by one returned unit | A threshold set too high delays alerts |
| Short hold for subscribers | Stock released to the public after subscribers had a chance | Loyal communities, limited drops | Usually manual work |
A rule of thumb for waves: alert a batch several times larger than the number of units available, because not everyone opens the message and not everyone who opens buys. Wait a few hours, check stock, then send the next batch. The right multiple depends on your store; start conservatively, see how many alerts became orders last time and adjust.
Practical safeguards
- Wait until stock is sellable. Receive and count the delivery and check the product is published and priced. An alert sent while a shipment is “on its way” sends people to a page they still cannot buy from.
- Set a minimum threshold so returns and inventory corrections do not trigger a send for one unit.
- Stop sending when it sells out again. Remaining subscribers stay on the list for the next restock.
- Say when quantities are limited. It is honest and helps people decide quickly.
- Mind your customers’ time zone. For SMS, some places also restrict sending times.
- Limit reminders. One follow-up a day or two later, only if stock remains and the person has not bought, is plenty.
Variants, bundles and discontinued items
Variants are where alert setups most often go wrong.
- One subscription per variant. A customer waiting for “Blue / Large” should not hear about “Red / Small”.
- Name the variant in the form and the alert: “Your Large Blue Linen Shirt is back.”
- Link to the variant, not just the product. Many platforms support a URL that preselects the variant, so the customer lands with their size already chosen.
- Partial restocks: alert only the people waiting for the sizes that returned.
- Bundles are only available when every component is. Tie alerts to the missing component or handle them manually.
- Discontinued variants. If a size or color will not return, send a short, honest note saying so, suggest the closest real alternative and close the requests. Our guide to sold-out and discontinued product pages covers what to do with the page itself.
If you know an item will return on a specific date and want to secure orders now, a preorder may suit you better. See preorders vs back-in-stock waitlists, including when to take payment.
What to put in the alert
Keep it short: the product name and variant with “is back in stock”, a photo, the price, one button linking to the preselected variant, a note if quantities are limited, a line explaining why they are receiving it (“You asked us to tell you when this item was back”), your store name and a way to opt out. A small “you might also like” line is common, but if the message reads like a newsletter, it no longer matches what the customer asked for.
Measuring results
| Metric | What it tells you | How to use it |
|---|---|---|
| Signups per variant | Which items people want most | Feed into reorder decisions |
| Signups per sold-out page view | Whether the form is visible and clear | If very low, test placement and wording |
| Clicks from alerts | Interest at the moment of restock | Low clicks may mean alerts came too late |
| Orders within a fixed window | Sales linked to alerts | Use the same window, such as a few days, every time |
| Unsubscribes and complaints | Whether messages feel welcome | A rise suggests too many reminders or off-topic content |
| Time to sell out after restock | How short supply was | Supports a larger order next time |
Be careful with attribution. Some people who received an alert would have bought anyway. Treat “revenue from alerts” as an indicator, not an exact figure, and compare like with like over time.
Using the waitlist for purchasing
While an item is out of stock, your sales history shows zero, which understates what you could have sold. Signups per variant help correct that: a size with a long waitlist deserves a bigger reorder. Our guide to reorder points and safety stock explains how to set reorder levels so items sell out less often in the first place. Our guide to managing inventory for product variants shows how to split a reorder across sizes using signups and sales.
Common mistakes
- Collecting signups per product instead of per variant.
- Treating an alert request as permission to send newsletters.
- Sending alerts before stock is received and buyable.
- Alerting hundreds of people for a handful of units without saying quantities are limited.
- Linking to the product without preselecting the variant.
- Leaving people waiting for a product that has been discontinued.
- Never looking at the signup data when reordering.
FAQ
Is a back-in-stock email a marketing email?
It depends on the content and on the rules where your customers live. A short message about the exact item the person asked about is generally treated as a requested message. Once it carries substantial promotion for other products, it looks more like marketing. Keep alerts focused and ask for marketing consent separately.
How long should I keep someone on a waitlist?
There is no fixed rule. Many stores close requests after a few months if the item has not returned, or send a short update asking whether the person still wants to hear. Whatever you choose, say so in the confirmation.
Do I need an app for back-in-stock alerts?
Not always. Some themes and email platforms include a basic version, and stores with a developer sometimes build their own. Apps typically add variant tracking, wave sending and reporting. Check what you already have before installing anything.
Bottom line
Back-in-stock alerts work best when they are specific, honest and timely: one request, one item, one clear message when it is genuinely available. Place the signup where the buy button would be, track it per variant, keep marketing consent separate, send in waves when stock is short, and use the waitlist to buy smarter next time.
