Why does "do you read me" mean "do you hear me"?

Solution 1:

The use of the word "read" in spoken radio transmissions was used to ask "how well is my message being received"

When using electronic voice communication, it is useful to know the quality of the signal being received. So the question "how (well) do you read (my transmission)" is asking for an indication of quality. The speaker wants to know if he needs to speak slower or louder to insure the message is received.

This is all part of voice procedure

Voice procedure communications are intended to maximize clarity of spoken communication and reduce misunderstanding. It consists of signalling protocol such as the use of abbreviated codes like the CB radio ten-code, Q codes in amateur radio and aviation, police codes, etc., and jargon.

A typical response might be "I read you 5 by 5" where the first number indicates the strength of the signal on a scale of 1 to 5 and the second number indicates the quality of the signal (how much noise there is).

"I read you five by five" means "I read you loud and clear" which implies "I hear and can understand everything you are saying"

Solution 2:

Besides its most popular meaning, read also means "to understand" or "to interpret". Consider the following examples:

• I read his actions as stemming from pure rage.
• He could easily read the fear in my eyes.

In radio (especially two-way) and telecommunication, words like roger, read and copy are used to clarify that communication has actually taken place. In potentially critical situations, the sender must always confirm their message has actually been understood and not just heard or read (in a literal sense). Examples:

• Roger that! We'll exit in five seconds.
• Agent 511, do you copy?
• Inspector! Inspector! Do you read me?
• Copy. Module will self-destruct in sixty seconds.

Several agencies and professions (e.g. aviation) have developed their distinct vocabulary for confirming the receipt and understanding of communicated messages.