Breastplate

 

The High Priest pressed on the gems (quartz) on the breastplate to transmit a message. In the same way we press on the keys of a phone or computer to transmit letters. 

Pressing a gem creates a piezoelectric charge.

Piezoelectric material, such as quartz, produces a small electric charge when you press on it. 

Exodus:

And they mounted on the breastplate four rows of gemstones:c

The first row had a ruby, a topaz, and an emerald;

11the second row had a turquoise, a sapphire, and a diamond;

12the third row had a jacinth, an agate, and an amethyst;

13and the fourth row had a beryl, an onyx, and a jasper.

 

https://link.springer.com/referenceworkentry/10.1007/978-3-540-72816-0_2897

(1) red jasper (sardius), (2) citrine quartz (topaz), (3) emerald, (4) ruby (carbuncle), (5) lapis lazuli (sapphire), (6) rock crystal (diamond), (7) golden sapphire (ligure), (8) blue sapphire (agate), (9) amethyst, (10) yellow jasper (chrysolite), (11) golden beryl (onyx), (12) chrysoprase (jasper).

What the actual stones were is disputed. I suggest that they were all piezoelectric.

The breastplate had 12 gems. 

They could have been:

7 buttons for consonants (one button has 4 letters associated with it, the others have 3)
3 buttons for vowels
1 button for end of letter (1 press), end of word (2 presses), end of message (3 presses)
1 button for correction

With the ark of the covenant and the breastplate with 12 buttons, it is possible to transmit the Hebrew alphabet. 

There are 22 consonants and 9 vowels. 

https://en.wikipedia.org/wiki/Hebrew_numerals

The system of Hebrew numerals is a quasi-decimal alphabetic numeral system using the letters of the Hebrew alphabet. The system was adapted from that of the Greek numerals in the late 2nd century BCE.

The current numeral system is also known as the Hebrew alphabetic numerals to contrast with earlier systems of writing numerals used in classical antiquity. These systems were inherited from usage in the Aramaic and Phoenician scripts, attested from c. 800 BCE in the so-called Samaria ostraca and sometimes known as Hebrew-Aramaic numerals, ultimately derived from the Egyptian Hieratic numerals.

The Greek system was adopted in Hellenistic Judaism and had been in use in Greece since about the 5th century BCE.[1]

In this system, there is no notation for zero, and the numeric values for individual letters are added together. Each unit (1, 2, ..., 9) is assigned a separate letter, each tens (10, 20, ..., 90) a separate letter, and the first four hundreds (100, 200, 300, 400) a separate letter. The later hundreds (500, 600, 700, 800 and 900) are represented by the sum of two or three letters representing the first four hundreds. To represent numbers from 1,000 to 999,999, the same letters are reused to serve as thousands, tens of thousands, and hundreds of thousands. Gematria (Jewish numerology) uses these transformations extensively.