Narrowband IoT (NB‑IoT), also known as LTE Cat NB1, is a standards-based Low Power Wide Area (LPWA) technology that works virtually anywhere. It simply and efficiently connects devices on already established mobile networks, and securely and reliably handles small amounts of fairly infrequent two‑way data. It provides very low power consumption, excellent extended range in buildings, easy deployment into existing cellular network architecture, network security & reliability and lower component cost.
For the Raspberry Pi Waveshare has developed this NB-IoT HAT. It uses SIMCom SIM7020E, which supports B1/B3/B5/B8/B20/B28. The SIM7020E can be controlled via serial AT commands. The HAT has a SIM card connector, USB (for power supply or debugging) and an UART to connect a host board like Arduino.
NB-IoT and LTE-M are very new services. Ask your mobile operator about availability of SIM cards, coverage, frequencies used and login procedures before you buy this product. See for example Deutsche Telekom IoT.
More information is available on the website of Waveshare.