If you’ve ever used a cell phone, you probably know about what a SIM card does. SIM stands for “subscriber identity module.” It’s how a carrier identifies that you are using a specific phone and what plan you’re using. Without it, the network doesn’t know that you are a subscriber, and they won’t let you use their service.

Standard SIM cards are physical disks that can slide into and out of a phone. So, if you want to change carriers for your phone, you eject the old SIM and insert the new one. It also works when you’re traveling overseas. Switch out a SIM, and you have international data. The same thing works when you buy a new phone. All you do is slip the SIM into the new phone, and it works. No fuss.

SIM cards work the same way they’ve worked since they were invented. They store your user profile and information about how to connect to the right network. They usually keep your contacts list, too, so you can easily switch that between phones. Sure, they’ve kept getting smaller over the years. The newest SIM, the nano-SIM is about a square centimeter, down from the first SIM which was the size of a credit card.

What is an eSIM?

So, how is eSIM different? The name stands for embedded subscriber identity module. Instead of using a physical card which you can slip in and slip out, it uses an embedded chip inside the device.

So, if you want to switch to a new carrier, there isn’t a SIM card to switch. Instead, the SIM part is embedded into the phone’s main board. There’s no card to switch. Instead, you can switch user profiles by rewriting the eSIM chip in the phone. Suddenly, it’s like you’re a new subscriber. New number. New plan.

The GSM Association, a group that represents the interests of mobile operators worldwide, says that eSIM will allow you to store multiple profiles on a device and switch between them remotely. It’s not just for phones, though. You can use it on any wirelessly connected device like a smartwatch, fitness band, or a health monitor.

eSIM will give device makers more options for design. If you don’t need to have a physical SIM slot, you can locate the chip anywhere in the phone. Phones may get thinner with smaller bezels. We’ll see what new designs manufacturers create.

What About Security?

If you think that sounds insecure, you wouldn’t be the only one. What would stop someone from using other people’s SIM’s to ride on their phone service or to listen in on their calls and texts? Or worse, could a hacker push a new profile onto your phone and take control of it?

eSIM’s are designed from the ground up with this in mind. When manufacturers make an eSIM device, they make sure that the only one who can send a new profile to the chip is the carrier itself. Carriers manage that through a server that they control. When your device requests a profile change, they use a unique key to verify that you are you.

eSIM will also help prevent device theft. With a removable SIM, it’s easy to switch profiles on a stolen phone. You just slip out the old SIM and insert another. Done. With eSIM, however, the thief can’t change the profile without the unique key. When the thief powers up the device, authorities will be able to instantly track it.

eSIM Support

The biggest roadblock to eSIM, however, is support. Without carriers having the system architecture to support eSIM, it doesn’t matter how great the technology is. You still can’t use it. According to The Verge, only ten countries currently support eSIM technology and only a few carriers in those countries.

In the US, T-Mobile, AT&T, and Verizon already support eSIM, but the smaller carriers do not. Sprint has plans to support the technology soon, but they haven’t released a specific timeframe. We will have to wait and see when the small-time carriers use that technology. Until then, if you want eSIM, you’ll need to switch to one of the big three.

The Internet of Things

One of the most exciting aspects of eSIM is how it can expand connectivity in devices beyond phones, smartwatches, and the like. Previously, if you wanted to connect your toaster to the internet (who doesn’t want fresh toast ready as soon as you get home?), you’d either need WIFI or a physical SIM to insert into a slot. That means getting a SIM card and then inserting it into the toaster. With eSIM, the retailer can automatically set your toaster up with your profile without messing with cards.

Automakers are especially interested in eSIM technology for connected cars. Imagine cars that will automatically switch to your profile by reading your phone and downloading your contacts and carrier. You’d be able to seamlessly switch out profiles. If you loan your car to a friend, you won’t have to worry about them using up all your data.

eSIM is a huge technological advance that could make the user experience better in our mobile devices, but it’s a huge advance for the internet of things. As more and more companies hop on board, we’ll see what that connectivity does for our homes and our lives. While the technology is still in its early stages, look for exciting things to come.