Identity & Recognition
Device Recognition
Device recognition means knowing that a browser or device has visited your site before, usually through a stored identifier such as a cookie. It tells you about the device and not necessarily the person, so shared devices and second devices both need separate handling.
October 31, 2026
Device recognition means knowing that a browser or device has visited your site before, usually through a stored identifier such as a first-party cookie. It tells you about the device, and you need something further to know the person using it.
How does a site recognize a device?
The usual method is simple. On the first visit the site stores an identifier in the browser. On a later visit the browser presents it and the site knows it has seen this browser before. How long that lasts depends on how the identifier was written and which browser holds it.
- A script-set cookie in Safari can be deleted after 7 days of browser use without interaction with the site, under Safari ITP.
- A server-side cookie often lasts longer on the same device, with exceptions.
- Clearing cookies or switching browsers ends it either way, even on the same hardware.
How is a device different from a person?
| Device recognition | Person-level recognition | |
|---|---|---|
| What it knows | This browser has been here before | This is a specific customer |
| Typical source | A stored identifier | A login, a tracked email click or a stored identifier linked to a profile |
| On a second device | Starts over | Can carry over once the person identifies themselves |
| On a shared device | Treats everyone as one visitor | Can be wrong if the last person's identity is still attached |
A recognized device only becomes a recognized customer once it has been linked to a profile at some point. Many recognized devices never get that link.
Why do shared devices matter?
A family tablet, an office laptop or a partner's phone can hold one person's identifier while someone else is shopping. For most on-site uses that's harmless. It starts to matter when a page displays something personal. Past orders on a shared screen can reveal things the customer wouldn't want shown, and some consumable categories are more sensitive than others. Match what you show to what you actually know, and save order history for a person-level signal, such as a login or an email click.
Why can't device recognition solve cross-device carts?
A shopper who starts on a laptop and opens your email on a phone is on a different device, so the laptop's identifier isn't there. The phone's browser may never have seen your store. Cross-device cart abandonment needs a person-level link, which an email click identifier or a store login can supply, and a cart saved on a server.
How does reOtter treat this?
reOtter recognizes people who've already given your brand their details, without a third-party network, in a record that doesn't depend on a browser cookie surviving. Its cart recovery page restores a saved cart on the device the shopper is using when reOtter has their cart and knows who clicked. When the click matches a customer, the page also greets them by name and shows Buy it again, with their past purchases and anything due. They don't need to log in.
Key takeaways
- Device recognition knows a browser has visited before, which is different from knowing who's using it.
- Shared devices are a reason to save personal details for a login or an email click.
- Moving to a new device takes a person-level link and a saved cart, because no device identifier follows the shopper there.
See how reOtter restores the cart → Abandoned cart recovery
Frequently asked questions
- What's the difference between device recognition and customer recognition?
- Device recognition knows a browser has been here before. Customer recognition knows who the person is, which takes a link to a profile through a login, an email click or a similar step. A device can be recognized with no person attached to it.
- Can device recognition work across devices?
- No. By definition it applies to one device, and a cookie never crosses devices. Linking a laptop and a phone takes a person-level connection, such as the same customer logging in or clicking an email on both.
- What about shared devices?
- A family tablet or shared laptop will look like one visitor. If a page shows personal details on device recognition alone, it could show them to the wrong person. Keep sensitive details such as order history for a person-level signal, such as a login or an email click.