Cellular IoT modules are small circuit boards that connect a machine, such as an electricity meter, a vehicle tracker or a card machine, to the mobile network. IoT stands for the Internet of Things: machines that send data over the internet without a person operating them. The module is soldered onto the machine's own circuit board.
A module holds everything the machine needs to reach the mobile network. At its centre is a cellular modem chip, which turns data into radio signals for the towers. The module adds the radio parts, the power control, a holder for a SIM card or a built-in eSIM, and its own small software. So the machine's maker does not need to design any radio. Its software sends simple text commands to the module, such as "connect" and "send this reading".
Machines are different from phones. A meter sends a few hundred bytes a day, not videos. It may need to run for ten years on one battery. And it may sit in a basement where the signal is weak. So there are special network types for machines. NB-IoT (narrowband IoT) and LTE-M send small amounts of data, reach deep inside buildings, and let the module sleep most of the time. Larger machines, such as vehicle trackers, use ordinary 4G. 5G adds a version for machines too.
Take, for example, a smart meter in the basement of an apartment block in Dwarka, Delhi. Its module uses NB-IoT. Every 15 minutes, the meter records how much power the flat has used, while the module stays asleep. Once every few hours, the module wakes up, connects to the nearest tower through the concrete walls, sends the stored readings in under a minute, and goes back to sleep. The power company receives the readings without sending anyone to the basement. India is replacing crores of old meters with smart meters, and many of them use cellular modules.
Each module must be tested and certified for the networks and countries where it will be used. Module makers do this testing once, so that each machine maker does not have to repeat it.
Once thousands of machines are connected, someone must manage their SIMs, data plans and failures. That is the job of IoT connectivity management. The machines' data then goes to an industrial IoT platform or to the power company's own systems. Some new modules can also switch to a satellite where no tower reaches, through direct-to-device satellite service.