Hide the method and leave people genuinely puzzled.
~$50Cost to start
ModerateDifficulty
15 min–1 hrTime / session
Is it you?
Nobody has scored this against your answers yet. 15 min–1 hr at a time, $50 to find out whether it sticks.
NoiseSome noiseSpaceTiny
2 setup steps, ~$50 all in. Nothing to buy until you say so.