eSIM Explained: How It Works, What I Learned Traveling with One
- Nico Dudli
- 4 hours ago
- 7 min read
Quick Answer
An eSIM is a digitally activated SIM built into your device as a permanent chip. Instead of swapping a plastic card, you install a mobile data profile via an app, QR code, or your device settings.
The biggest advantage for travelers: your existing number and home SIM stay in the device while you use a separate data plan for your destination.
What Is an eSIM?
An eSIM (Embedded SIM) is based on a chip permanently built into your device — technically called an eUICC (Embedded Universal Integrated Circuit Card). Mobile profiles are loaded onto this chip digitally.
You no longer need to insert a physical SIM card. Depending on the provider, setup works via an app, QR code, activation code, or directly through your device settings.
How many profiles can be active simultaneously depends on your specific device.
Who Sets the eSIM Standards?
The technical foundation for consumer eSIMs comes from the GSMA, the international trade body for the mobile industry. Their standards define how digital profiles are securely provisioned and managed.
The core mechanism is called Remote SIM Provisioning (RSP): a mobile profile is encrypted and transferred over the internet to a compatible device via an SM-DP+ server, which handles secure delivery and installation.
How to Set Up an eSIM
The process is similar across most providers:
Choose a provider and data plan
Install the eSIM via app, QR code, or activation code
Label the profile in your mobile settings
Set the eSIM as your preferred data line
Enable data roaming for the travel eSIM at your destination
My most important tip: Set up the eSIM before you leave — at home, over Wi-Fi. Take a screenshot of the setup details, save your order number, and double-check which SIM is selected for mobile data.
Most eSIM issues aren't technical failures — they're settings problems: wrong data line selected, roaming not enabled, or APN not configured. On some Android devices, manual APN configuration may be required.
Full iPhone setup guide: How to Set Up Saily eSIM on iPhone
Full Android setup guide: Saily eSIM Android Setup
eSIM vs. Physical SIM
Feature | Physical SIM | eSIM |
|---|---|---|
Installation | Insert card | Load profile digitally |
Multiple profiles | Depends on SIM slots | Multiple profiles storable |
Device switch | Swap card directly | Depends on provider |
Loss | Card can be lost | No removable part |
Travel use | Local SIM or roaming | Buy and install before departure |
Which Devices Support eSIM?
Not every device is compatible — always check before buying a plan.
Apple iPhone: eSIM has been supported since the iPhone XS/XR (2018). I personally use an iPhone 15 Pro with multiple profiles stored. iPhones sold in mainland China typically do not support eSIM.
Android: Many current Samsung Galaxy S/Z series and Google Pixel devices support eSIM — but compatibility varies by region and carrier. Tip: dial *#06# — if an EID appears, your device has an eSIM chip.
Tablets, Watches, Laptops: Select iPad Cellular models, Apple Watch, and some Windows devices also support eSIM.
Dual SIM: Two Plans, One Device
On a Dual SIM-capable smartphone, you can run your home SIM and a travel eSIM simultaneously.
In practice:
Your home number stays active for calls, texts, and two-factor codes
Mobile data runs through the travel eSIM
WhatsApp and other messengers keep working with your existing number
This is the setup I use on every trip. One caveat: even with data roaming disabled on your home SIM, calls or SMS may still incur charges depending on your plan. Check your carrier's terms before leaving.
Real-World Experience: What I Actually Tested
I've been using travel eSIMs regularly for several years — across Europe, Asia, and North America. Here are the situations that showed me what the technology can and can't do.
Teaching an Online Class on Mobile Data
One of my most demanding tests was in Port de Sóller, Mallorca. I ran a live online class with around 25 participants — video, audio, screen sharing, continuous connection. The connection held for the entire session. That matters more to me than any speedtest, because a dropout would have been immediately visible to everyone in the room.
Hotspot for Multiple Devices
In Montpellier, I used the eSIM as a hotspot for two MacBooks and two smartphones simultaneously. In the city center I measured up to 354 Mbps download. At a café it was 70.94 Mbps — enough for video calls and agency work across multiple devices.
Full report: Saily eSIM France Review
Road Trip Navigation
In Austria and Portugal I used the eSIM mainly for navigation, messaging, and travel planning. Connection was reliable on the routes I drove. In mountain valleys and remote areas, coverage can still drop — that's a network infrastructure issue, not an eSIM issue.
More on European coverage: Saily eSIM Europe Review
Trains and Network Reality
Germany gave me the clearest lesson in what an eSIM cannot do. In Munich city center I hit 183 Mbps at Marienplatz. On an ICE train between Hannover and Hamburg, peak speed was 54.6 Mbps — with significant drops throughout the journey.
The key takeaway: An eSIM simplifies access to a local network. It cannot create coverage where the local carrier has none.
Speedtest Overview
Location | Download | Upload | Network |
|---|---|---|---|
St. Gallen, Switzerland (Salt) | 271–370 Mbps | — | 5G |
Montpellier, outdoor | 354 Mbps | 35.9 Mbps | 5G |
Munich, Marienplatz | 183 Mbps | — | 5G |
Bangkok | 84 Mbps | — | 5G |
Alpstein, ~1,500m | 34–65 Mbps | — | LTE |
Saint-Guilhem, France | 23.2 Mbps | 8.63 Mbps | LTE |
Switzerland deep-dive: Saily eSIM Switzerland Review
Which Travel eSIMs I Use
For my own trips I rely on two providers:
Saily is my main choice for Europe, Asia, and North America. I've tested it in over twelve countries including Switzerland, France, Germany, Italy, Spain, Portugal, Thailand, Vietnam, Singapore, and the UAE. Plans are available for 200+ destinations, including regional plans for Europe and North America.
With code TECHNOVICE you get:
35% off Saily North America Regional Plans (USA, Canada, Mexico) — e.g. 20 GB for $35.74 instead of $54.99 (verified June 12, 2026)
10% off all other eligible Saily plans worldwide
→ Saily with code TECHNOVICE
Full plan breakdown: Saily eSIM Plans 2026 · All discount codes: Saily Coupon Codes 2026
Holafly is my second option, especially for destinations outside Europe. Holafly offers unlimited data plans for many destinations — useful when you can't predict how much data you'll need.
With code NOVICE you get 5% off your Holafly plan.
Both providers work on the same principle: buy, download via app or QR code, done. Which one fits better depends on destination, data needs, and budget.
Direct comparison: Holafly vs. Saily · Saily vs. Airalo
Pros of an eSIM
Fast setup: Buy and install before you leave, no store visit needed
No physical card: Nothing to lose, swap, or search for
Home number stays active: Calls, texts, and two-factor codes keep working
Multiple profiles: Store several and switch by destination
Regional plans: One plan for multiple countries, no SIM swap at every border
Hotspot capable: Share your connection with laptops and other devices
Predictable cost: Price, data, and validity known before you travel
Cons of an eSIM
Not every device is compatible: Older and some regional models lack eSIM support
Device switching is harder: Travel eSIMs often can't be transferred to another device
No local phone number: Most travel eSIMs are data-only — no calls or SMS via the eSIM number
Needs internet to install: Wi-Fi or an existing connection required for profile download
Settings errors block connection: Roaming, data line selection, and APN must all be correct
Local performance not guaranteed: Travel eSIMs use partner networks — quality depends on local infrastructure
Frequently Asked Questions
Can I transfer an eSIM to a new device?
For regular carrier plans, often yes. For travel eSIMs, reinstallation on a different device is usually restricted or not allowed. Don't delete a profile before checking your provider's terms.
Will the eSIM connect automatically after landing?
Usually yes, if set up correctly. If not: Is the eSIM enabled? Selected for data? Is roaming on? Is the APN correct? A quick flight mode toggle often helps.
Is an eSIM more secure than a physical SIM?
If your device is lost or stolen, the eSIM can't be removed and used in another phone. Profile management follows standardized security protocols. That said, an eSIM doesn't protect against phishing, compromised accounts, or an unsecured device.
Do I need internet to set up an eSIM?
Yes — you need Wi-Fi or an existing connection to download the profile. Set it up at home before you travel.
Do I need to enable data roaming?
For most travel eSIMs, yes — because the eSIM connects to a local partner network. Make sure you only enable roaming for the travel eSIM, not accidentally for your home SIM.
Can I use the eSIM as a hotspot?
Usually yes, though terms vary by provider and plan. I've used Saily as a hotspot for up to four devices simultaneously.
Does an eSIM improve signal strength?
No. The SIM format has no effect on reception. Signal quality depends on the local network, your location, and your device.
What if I have signal bars but no data?
Check: Is the travel eSIM selected as the data line? Is roaming enabled? Is the APN correct (especially on Android)? Toggle flight mode, then retry.
Conclusion
An eSIM has become a standard part of how I travel — not because every connection is automatically fast or cheap, but because the setup is simple and my existing number stays active throughout.
What an eSIM can't do: fix local dead zones, improve weak infrastructure, or correct settings you haven't configured. The right settings matter as much as the plan you buy.
The tests that convinced me weren't the highest speedtest numbers. They were the situations where the connection had to work: a live class with 25 participants on Mallorca, a four-device hotspot in France, navigation across Portugal and Austria.
That's where a travel eSIM proves its value — or doesn't.
For general travel app recommendations beyond connectivity: Best Travel Apps 2026
About the Author
Nico Dudli is a digital entrepreneur, lecturer in Marketing and Digital Technologies, and the founder of TechNovice. He has tested travel eSIMs across more than 12 countries on two continents — from running live online classes in Mallorca to managing a four-device hotspot in the south of France.
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