The guys behind Project Black Mirror have recorded brain wave activity with ECG pads, matched the incoming patterns to pre-saved digital patterns saved on a MacBook, then fed the matched commands to a speech synthesizer chip that translates the command to Siri. This way you can give Siri commands without talking or touching the screen of your iPhone 4S. A full “How they did it” and movie can be found after the break.

How we did it !
1. ECG pads provide raw skin conductivity / electrical activity as analogue data (0-5v).
2. This is plugged into the Arduino board via 4 analogue inputs (no activity = 0v, high activity = 5v).
3. The Arduino has a program burnt to its EPROM chip that filters the signals.
4. Josh trained the program by thinking of the main Siri commands (“Call”, “Set”, “Diary” etc.) one at a time and the program where we captured the signature brain patterns they produce.
5. The program can detect the signature patterns that indicate a certain word is being thought of. The program will then wait for a natural “release” in brain waves and assume the chain of commands is now complete and action is required.
6. The series of commands are fed to a SpeakJet speech synthesiser chip
7. The audio output of which simply plugs into the iPhone’s microphone jack.

So simple, we still can not believe it really works

Source [9to5mac]