A dated letter opener is a tool used to open letters, typically from the past. It is also known as a SIRS, which stands for 'Slit-In-Ribbon-Strip'. This tool is used to open envelopes without damaging the contents inside. It is usually made of metal and has a sharp blade that is used to cut through the ribbon or paper on the envelope. The dated letter opener is an essential tool for archivists and historians who need to access documents from the past.