Efficient waiting for user input

Projects Programming
1

What is the most resource efficient way of waiting for user input from a serial connection? Currently, I am using:

while (Serial.available()==0){}

and was wondering if this is the best option. The Arduino could be waiting for hours on battery power in an autonomous vehicle for a command so I am interested in using as little power as possible.

3

BTW I am currently using an Arduino Nano

4

Hardware tricks are required to wake the ATmega328 up from sleep, upon UART character reception.

Here is one discussion: Put ATmega328 in very deep sleep and listen to serial? - Arduino Stack Exchange