Methods for confirming on both sides that a signal was received in one direction
Mmm! The usual way mimics the way we exchange information ourselves. "Here is a message to which I will need a response. The message is "lock the doors when you get my OK." One good way for the car to respond would be to send back the same message but with an ACK1 code attached. It is waiting now for the remote to repeat the command perhaps with a slightly different ack2 code. For something like remote door closing flashing the car lights is a good way in practice of indicating that the message has been actioned.

However I think you have in mind something much more critical than car door locking &amp; unlocking in mind. How about "landing gear locked down" on an aircraft?

These systems are called open &amp; closed loop. An open loop just carries out the action. There are many ways in which a message can be checked for its authenticity. The addition of check characters at the end is once such method. Cyclic Check Character (CCC) or Block Check Character (BCC) are ways of counting say, the number of "ones" in a digital message. A bit like counting the numbers of "A's" in a text would give you a better check on integrity. 

At the end of the day if of vital importance the message can be sent twice or more times and compared to make sure it is faithfully received. {faithfully received - faithfully received}! It will not be actioned until a previously agreed number of similar messages are exchanged.

I hope this opens up the possibilities of how it is possible to proceed with pretty near bombproof security and authenticity and answers your query sufficiently. 

This in no way considers the question of interception or rogue generation of commands. That is more within the sphere of cyphers &amp; codes - a rather different ballgame.