This is not true. 2015 BMW X3 Run-flat tire but no TPMS in tires.
TPMS = Tire Pressure Monitoring System
These system has 2 styles:
1) direct; and
2) Indirect
Feature of DIRECT TPMS is having a sensor mounted on the rim.
Feature of INDIRECT TPMS is not using a sensor, but used either
a) speed sensor; or
b) levelling sensor;
INDIRECT speed sensor style measure the rotational speed on each wheels to determine whether enough pressure inside the tire
INDIRECT levelling sensor style measure he height between tires to determine whether tires has enough pressure.
DIRECT style usually can check actual psi value inside the tire whereas INDIRECT only knows there is different in pressure.
2015 BMW X3 uses INDIRECT speed sensor style. So you won't find any sensors inside the tire.