piezo electric and electret throat mic

There are basically two types. piezo electric and electret .

Piezo electric us a small thin ceramic disc 10-20mm diameter which is silver plated on each side, this disc is held firmly at the periphery and has a small spring that connects  the center of the piezo disc  to the thin flat plastic diaphragm that rests against the users skin. vibrations  in the diaphragm travel through the connecting spring to induce voltage across the silvered sides of the piezo disc. The high impedance  electrical output of the vibrating piezo disc is transformed to a much lower operating impedance by a single transistor stage , hence like the electret based throat mic , the piezo too requires a few milliamps of current at  a few volts to work. Piezo electric throat mics tend to have a higher frequency spectra output with not so many low frequencies , however they tend to have a narrower more peaky frequency response, no doubt related to physical resonance properties of the piezo element  so they can sound quite tinny and un natural , I have only found one brand of piezo based throat mics that puts out what I would call adequate  communications quality audio.
This unit However is electret mic based, the mic is  in a pressure chamber that sits against the neck , there is a sealed chamber under the large skin contact diaphragm and the much smaller electret mic diaphragm , this sealed chamber acts much like a "pneumatic"  diaphragm movement  amplifier  . Hence small movements of the throat skin diaphragm cause a much larger movement in the electret diaphragm in the ratio of their surface areas.  Electret mics have a very flat frequency hence this mic has quite a flat output. The  throat tends to attenuate a lot of the high frequencies  more so than the low frequencies,  I guess the speech is formed at the lips and tongue  so has to travel back down the throat or though the  flesh .
This mic has a small single  earbud type earphone on a length of thin fexible cable , the earphone can be worn under a ear defender if necessary and not destroy the acoustic isolation , The cable has a PTT button in series with the electret mic with a provision to switch the PTT permanently on , the mic and speaker are terminated in a  2.5mm  stereo plug and 3.5mm mono plug respectively