In recent years, “silent” instruments have become popular for people to be able to practice their instruments without making a lot of noise. They’re not really silent but rather are things like acoustic guitars and violins that don’t have much in the manner of resonating bodies, but do have headphone amplifiers. They still make some noise but if you’re practicing in a bedroom or hotel room, it’s not going to bother anyone.
If you have an amplifier with a headphone output, you can use the HarmonicasterTM “silently”. You’ll be able to hear the amplified tone, but everyone else will hear just unamplified acoustic harmonica.