Medical Definition of adhesive. 1: an adhesive substance; especially : a substance (as glue, starch, paste, or mucilage) that bonds two materials together by adhering to the surface of each.
The sensors physically measure the tire pressure in each tire and report it to the vehicle's instrument cluster or a corresponding monitor. Some units also measure and alert temperatures of the tire as well. These systems can identify under-inflation in any combination, be it one tire or all, simultaneously.
There is a sensor and wireless link in each of the four tires in a direct TPMS equipped automobile. Most TPMS sensor systems can handle up to ten tires. The sensor monitors the tire pressure and sends out alerts when the pressure drops below a preprogrammed threshold (typically something like 10% of rest pressure). In the US, the TPMS system operates at either 315MHz or 433MHz, both in the ISM band, so they can be unlicensed. The signal is encoded, but not encrypted. The signal is either ASK of FSK modulated (essentially it looks pretty much like a garage door opener).