Then, what is the most important contrivance?

Radios built-in, apparantly.
Nowadays, Japan is being invaded by many foreigners.
And many Japanese have been killed secretly and replaced by their resemblances, their lives, houses, salaries, families, names and savings robbed.
How can such violences be?
How can so many criminals have not been discovered?
One answer for this question is that radios built-in may be very effective for them to become a native Japanese speaker.