IOT stands for "Internet of Things". Some folks seem to believe that everything has to be monitored so that its readings can be published on the Internet. Any sensor can be used: temperature, pressure, velocity, light intensity, force, etc. The sensor is connected to a microcomputer that digitizes the readings. In turn, the microprocessor is connected to a low power RF transceiver, which gains Internet connectivity through a local WIFI router. Fairly capable 32-bit microprocessors are now very small and require little power to operate. Capable enough to handle the rather gigantic message protocol used over WIFI.
There are web sites to which sensors can send data, and those same sites present that data on a web page.