The Virgil Practice Clavier, named after his inventor, Almon Kincaid Virgil, and advertised as a “silent piano” was very popular with teachers and pianists during its heyday (from 1888 to 1913). Claudio Arrau – amongst others – owned one and was a great believer in its merits.
It is basically a complete keyboard mechanism but nothing else. Each key makes a clicking noise when you press it with the correct touch. No click means your touch is sloppy. You can also adjust the weight of each key (from 2 to 20 ounces) so that you can use the clavier for developing finger strength (they believed in this sort of thing 120 years ago!).

The basic idea (besides not bothering the neighbours) was that you could shorten the period of study by doing away with tone, so that the finger technique is acquired mechanically an unmusically, while value of tone, reading, expression, whatever we understand by musical production exciting our receptivity through the ear, is delayed until the player's hand is formed and considerably developed. (yes, that is what people believed 120 years ago – but I for one am not sure that there isn’t some validity to this argument).

Have a look at a picture of an original Virgil Clavier here:
https://www.galwest.com/collectibles/assorted/practice_clavier.htmFor an interesting historic perspective on practice and the use of the Virgil clavier, look here:
https://www-personal.ksu.edu/~vhouser/etude.htmUnfortunately (but I may be wrong here) I don’t think they are manufactured anymore, and you can only get one as an antique. It may or may not be in good working order. It may be very expensive just because it is considered an antique.

Here they have one selling for US$ 400:
https://www.musicianshotline.com/classifieds/0603/keyboard.htmOne of the reasons, I believe, they are note manufactured any more, is that for the price of a Virgil Clavier, you may as well buy a digital piano, and switch it off! Ad when you finish your silent practice, just switch it back on. If you disagree with the basic Virgil contention that playing without sound is beneficial, but still do not want to upset the neighbours, just use headphones with your digital piano. So it seems that digital pianos largely replaced these silent claviers.
Best wishes,
Bernhard.