In this guide
- Deterministic cross-device tracking links devices through something the person gave you: a login or an e-mail.
- Probabilistic methods guess from signals like IP address and behaviour. They are less accurate and less privacy-friendly.
- A store can do a lot with User ID in GA4, hashed e-mail in server events and logged-in platform audiences.
A customer sees your ad on their phone on the train, researches on a laptop at work and buys on a tablet at home. A browser-based tool sees three strangers. Cross-device tracking is the effort to see one person. It is possible in specific ways and impossible in others, and the line is set by privacy rules and browser limits. This page explains the methods and what you can realistically do. See also cross-session user stitching and attribution tracking.
Two approaches
| Approach | How it links devices | Accuracy | Privacy |
|---|---|---|---|
| Deterministic | The same login, e-mail or customer ID on each device | High | Needs consent and a clear purpose |
| Probabilistic | Statistical matching of IP address, location, time and behaviour | Lower | Harder to justify under privacy rules |
Works with your stack
Grab a logo and throw it. These are the tools Open Tracked already talks to.
Where deterministic linking happens
Ad platforms
Meta and Google know who is logged in on each device, so they link devices for their own users. That is why the platforms can show a cross-device view that you cannot build yourself.
02GA4 with User-ID
If you send a non-personal user ID when someone logs in, GA4 can combine their activity across devices in reporting.
Your CRM and shop
A customer account, an e-mail address and an order history link devices naturally.
04Server-side events
A hashed e-mail sent with each event lets platforms match the same person on different devices.
What a store can do
Encourage login
Accounts, wish lists and saved carts give people a reason to sign in.
Send User-ID to GA4
A non-personal customer ID on login.
Send hashed e-mail with server events
On checkout and lead events, with consent. See event match quality.
Use your CRM as the source of truth
Customer-level reports show devices as one person.
Do not try to guess identities
Probabilistic matching is hard to justify and often inaccurate.
Orders from your store, back to the ad that earned them
Your store sends the order once. Open Tracked passes it on to each ad platform, cleaned and deduplicated.
What Open Tracked does and does not do
Open Tracked's User ID power-up creates an anonymous ID for each visitor, based on their address, browser and your tagging host. It changes when one of those changes, so it is a per-browser identifier, not a cross-device one, and it is never used as the GA4 User ID. For cross-device recognition, use a login-based key in the Enricher (it can use a User ID you send) and send hashed e-mail with your events. The Data Store then remembers the hashed identifiers for returning visitors.
Limits to accept
- Visitors who never log in or give an e-mail stay separate devices.
- Browser privacy features limit what any tool can link.
- Consent is needed to link devices for advertising in the EU and UK.
A realistic example
A furniture store finds that many customers start on a phone and buy on a laptop. In its ad reports, phone ads look weak, because the sale is credited to the laptop session, often as direct traffic. The store asks customers to create an account at checkout, sends a non-personal user ID to GA4 on login, and sends hashed e-mail with every purchase to Meta and Google. After a few weeks, reports for logged-in customers show the phone visit that began the journey, and the ad platforms report more purchases for the same spend, because they can match the sale to the earlier ad view. The store did not buy any device graph. It gave customers a reason to identify themselves and passed that identity on carefully.
Check your tracking in one pass
This is an example. Run the check on your own site to see where yours stands.
Frequently asked questions
What is cross-device tracking?
Linking a person's activity across their phone, laptop and other devices.
How accurate is it?
Deterministic methods based on logins and e-mail are accurate for people who identify themselves. Probabilistic methods are less so.
Can GA4 track users across devices?
Yes, with User-ID for logged-in visitors, and Google signals where available and allowed.
Does Open Tracked's User ID power-up link devices?
No. It is an anonymous per-browser ID. Use a login-based key and hashed e-mail for cross-device recognition.
Is cross-device tracking allowed?
With a lawful basis and usually consent. Ask your advisor.
Do I need spreadsheets to read my results?
No. Once tracking is live, the Open Tracked analytics shows spend, revenue, ROAS and profit, and you can ask Ari, the built-in AI assistant, questions about your own numbers in plain words. Ari's allowance depends on your analytics plan.
Is Open Tracked different from Open Track or Open Space Track?
No. Open Tracked is the official name of our server-side tracking platform, and the website is opentracked.io. Many people search for it as Open Track, OpenTrack or Open Space Track. All of them lead to the same product: server-side Google Tag Manager hosting, first-party analytics and a CRM pipeline.
Fix your tracking at the source
Open Tracked hosts your server-side Tag Manager, keeps first-party cookies alive and shows what each ad is really worth.
The Open Tracked team
We build Open Tracked: server-side tracking hosting, analytics and the tools around them, for stores that spend on ads. Questions about this guide, or an idea for the next one?
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