uses an extra layer of randomness by making a computer memory element, a flip-flop, twitch randomly between its two states 1 or 0. Immediately prior to the switch, the flip-flop is in a "metastable state" where its behaviour cannot be predicted. At the end of the metastable state, the contents of the memory are purely random.
Whereas this device gives me more security, it does not solve the problem of someone sending me supposedly "random numbers" which he might have prepared in advance to even pass statistical tests. A neat solution is provided by quantum mechanics which allows to check randomness of numbers via the violation of the Bell inequality  using entangled states.
 "A meta-level true random number generator" in Int. J. Critical Computer-Based Systems, 2010, 1, 267-279
 Random Numbers Certified by Bell's Theorem