A SIM (subscriber identity module) is what allows your phone to connect with a mobile network to send and receive messages, access data services and make voice calls. This little chip has reduced in size over the years (from mini to micro and nano), but can still be too big for some devices that need network connectivity, such as the forthcoming Apple Watch series 3.

The solution lies in what is called an eSIM, with “e" standing for embedded. This is a chip embedded within a device. This technology means that thinner and smaller devices can connect to a mobile network. If the eSIM is used on a wearable such as an Apple Watch or a computing device, it is easy to get your service provider to replicate your phone number on the secondary device.

India will be seeing the eSIM technology, supported by Airtel and Reliance Jio, for the first time, with the Apple Watch series 3 arriving in stores this weekend.