Wikipedia
A stenomask is a hand-held microphone built into a padded, sound-proof enclosure that fits over the speaker's mouth or nose and mouth. Some lightweight versions may be fitted with an elastic neck strap to hold them in place while freeing the user's hands for other tasks. The purpose of a stenomask is to allow a person to speak without being heard by other people, and to keep background noise away from the microphone.
A stenomask is useful for speech recognition applications, because it allows voice transcription in noisy environments. Perhaps more importantly, a stenomask silences the user's voice so that it does not interfere with the surrounding environment such as a court or a classroom. The user can verbally identify the speaker, indicate gestures and unspoken answers, and describe activities as they take place.
An operator of a stenomask can be trained to "re-voice" everything he or she hears into a stenomask connected to a speech recognition system, for a real-time text transcription of everything spoken. This allows a "voice writer" to produce instant text feeds within a courtroom and distribute them in plain text format immediately after a proceeding. The equipment can also interface with litigation management software.
A trained operator using a stenomask connected to a pre-trained speech recognition system can exceed 180 words per minute while at the same time exceeding 95 percent accuracy. They may also modify the pronunciation of the words they are speaking in order to improve accuracy.
Microphones that work much like a stenomask are used by aircraft ground crews to communicate with cockpit crews in airport environments with extreme engine noise, and are usually part of their headsets.