Narrowband Internet of things (NB-IoT) is an LPWAN (low-power wide-area network) standard that is focused on coverage indoors and in places where other technologies have more difficulty in terms of coverage.
The technology is well suited for battery-powered devices that typically send updates with a smaller amount of data per day and in between saves energy so that the battery life can be upwards of 10 years.
Devices with NB-IoT are significantly easier to implement and thus provide cheaper solutions for IoT solutions compared to LTE-M.
In NB-IoT, part of the LTE standard is used, but the bandwidth is limited to 200kHz. Alternative names depending on the 3GPP (3rd Generation Partnership Project) release version are LTE Cat NB1-2.
NB-IoT uses half duplex and with a power of 14/20/23 dBm depending on the version. Devices with NB-IoT usually use e-sim which is part of the solution.
Some devices can also offer support for several Telecom companies in their configuration so that customers do not have to tie themselves up with one provider.
Telecom companies IoT services often offer a user portal where you can see how individual devices communicate and administer the subscriptions that are offered.