The Elitzur–Vaidman bomb-tester, specifically (https://en.wikipedia.org/wiki/Elitzur%E2%80%93Vaidman_bomb_tester).

Next, that I can buy and program a computer for 0.30 USD that's half the size of a grain of rice (ATtiny10). There are cheaper too, but that's the one I like.

Finally, on to the horrifying: Boltzmann brains. The idea that given a reasonable interpretation of the laws of thermodynamics, and long spans of time, the most common form of brain in the universe ought to be one that forms due to random fluctuations. It exists for long enough to have exactly one thought (e.g. recall a false memory), then dissipates.

This ought to be by far the most common form of conscious mind in the Universe. In a sense, you could say it 'blows' the general case of minds.

Since you are a mind, statistically, you ought to be a Boltzmann brain. You may not be, but are unable to prove otherwise, even to yourself. So either we have some things left to learn about thermodynamics, or the most probable outcome at all times is that you cease to exist immediately after having your current thought (although I hope you don't). Sleep tight!