By pointing your Internet Browser at

https://www.gov.uk/government/publications/construction-industry-scheme-cis-340/construction-industry-scheme-a-guide-for-contractors-and-subcontractors-cis-340

you can see online this Government Tax Scheme in its entirety:-

As far as our sector of the service industry is concerned we are mentioned in section A.31 “Installation of security systems that are dedicated to security only is excluded from the scheme. Specific types of systems specifically mentioned in the legislation are burglar alarms, closed circuit television and public address systems. Preparatory works on the land such as digging, building/erecting concrete posts on which to install the closed-circuit television (CCTV) is within CIS.”