Smart Site Safety System (4S): a practical guide for Hong Kong contractors
By Niall Dorr, founder of ImageDeep · Updated 26 October 2026
Hong Kong's Smart Site Safety System, or 4S, uses smart devices and a central platform to watch high-risk work on construction sites in real time. It is mandatory on larger public works and, for some activities, on private building works. This guide covers what 4S is, who must use it, how the 4S Labelling Scheme and CITF funding work, and where AI cameras fit.
What is 4S?
4S combines smart devices such as AI cameras, sensors, smart locks and wearables, a communication network, and a centralised management platform. Together they let a site monitor high-risk work such as lifting operations, confined space work and mobile plant, raise alerts early and keep a record of what happened.
Who must adopt 4S?
Public works
Since February 2023, public works contracts with a contract sum above HK$30 million must fully adopt 4S, under Development Bureau Technical Circular (Works) No. 3/2023.
Private building works
Since July 2024, the Buildings Department requires the 4S Mobile Plant Alert System and Tower Crane Alert System for building works estimated above HK$30 million that use mobile plant and tower cranes. The condition is imposed when superstructure plans are first approved, or on major revisions.
Extended in July 2025
The requirement now also covers demolition, excavation and lateral support, foundation and site formation works.
What 4S usually covers
- Centralised management platform
- Digital permit-to-work
- Mobile plant and tower crane danger-zone alerts
- AI alerts for unsafe acts such as missing PPE
- Confined space monitoring
- Smart wearables and e-locks
The exact set depends on your site's risk assessment. Where a high-risk activity is not covered by 4S, the CIC expects a justification, such as an alternative measure proposed by the safety officer.
The 4S Labelling Scheme
Launched in May 2024 by the Development Bureau and the Construction Industry Council (CIC). The main contractor applies, with the developer's or owner's consent. The CIC inspects the site, normally within a month of the application; labelled sites display a 4S plaque and are listed on the CIC website. The CIC also makes surprise inspections and can withdraw a label if 4S is not properly used. Application and renewal fees are waived for submissions made on or before 31 December 2026, and a 4S device does not need to be on the CITF pre-approved list to qualify.
Funding through CITF
The Construction Innovation and Technology Fund (CITF) subsidises 4S. Since May 2024 it also covers network upgrades and extra manpower to run and maintain 4S, and from late 2024 local mobile plant and tower crane rental companies can claim up to HK$7.5 million each for danger-zone alert systems. In 2026 the Government injected HK$1 billion and the CIC HK$400 million into the fund.
Is it working?
According to the Government, about 60% of new construction and maintenance projects above HK$30 million have adopted 4S and received labels, and the construction industry's overall accident rate fell by about 20% from 2023 to 2025.
Where Scopis AI fits
Scopis AI is listed as a 4S product. It adds AI safety monitoring (PPE, fall and danger-zone detection), mobile plant and tower crane danger-zone alerts, and a centralised management platform to the cameras you already have, with a trained operator in our Tuen Mun centre checking every alert.