NSI Technical Bulletin No. 0021 provides guidance on the implementation of BS 8243:2010, which outlines the installation and configuration of intruder and hold-up alarm systems (I&HAS) designed to generate confirmed alarm conditions. The document details significant changes from the previous standard, including mandatory requirements for hold-up alarm confirmations under certain conditions, updated definitions, and specific design and installation recommendations aimed at minimizing false alarms. Compliance with these guidelines is essential for organizations seeking to maintain NSI approval for electronic security systems. Manual review is recommended for complete details.