From any number of sources one can buy, quite cheaply, high-quality electret condenser microphone elements. The critical thing for you, the hacker, to understand at this point is that electret microphones require a small amount of externally applied voltage, typically from a battery, in order to function. Electret microphone elements can usually be powered by a wide range of voltages. Occasionally one finds electret elements with three wires instead of two. The issue of packaging is not merely aesthetic: the shape and mass of the material can affect the frequency response and directionality of the microphone. “Binaural recording” is a microphone technique optimized for playback over headphones: two small microphones are mounted in the ear canals of a specially designed dummy head or worn like earbuds in the outer ear of the recordist; when the recording is played back over headphones, there is great 3D spatial realism because the headphones are in the same spatial relationship as the mikes were.