This document summarizes three common techniques for error detection in computer networks: parity check, checksum, and cyclic redundancy check (CRC). It provides examples of how parity check works by adding an extra bit to make the number of 1s either even or odd. It explains that checksum involves dividing data into segments, adding the segments, and sending the complemented sum. CRC is described as a more powerful technique that is based on binary division, where a remainder at the destination indicates an error.