You've seen them online: tiny plugs you stick into your laptop's headphone jack to "block" the microphone. But do they actually work?
The Theory
These "mic blockers" are essentially dummy headphone plugs. When you insert them, your laptop thinks you plugged in a headset. It switches the audio input from the internal microphone to the (non-existent) headset microphone. Result: the computer records silence.
The Flaw
This trick works on older laptops. However, modern smartphones and MacBooks are smarter. They can detect that the plug has no electrical resistance (no actual mic attached) and will often default back to the internal array.
Furthermore, malware can override this software switch and force the internal mic to stay on regardless of what is plugged in.
The Real Solution
Physical isolation is the only guarantee. If you are having a top-secret conversation, leave your electronics in another room. No app or plug is 100% hack-proof.