Construction attendance registration — NSSO
What is Checkinatwork (CIAW)?
Checkinatwork — also written as Check In at Work and abbreviated to CIAW (sometimes CAW) — is the mandatory electronic attendance registration of the Belgian National Social Security Office (NSSO, known locally as RSZ/ONSS) on large construction sites. Every person who comes to work on the site must be registered. On this page we explain exactly what CIAW is, who it applies to, what the fines are and what changes in 2027.
Why does Checkinatwork exist?
The government wants to know at any moment who is present on a construction site — to fight social fraud and undeclared work and to make sites safer. That is why every attendance has to be reported electronically to the NSSO. This site registration runs through the online service Checkinatwork, which has existed since April 2014.
Who has to be registered?
The CIAW requirement applies to sites with a total value of €500,000 (excl. VAT) or more. If your site is above that threshold, everyone who works on it must be registered:
- Your own employees
- Self-employed workers and freelancers
- Subcontractors (at every level)
- Safety coordinators
- Site managers and supervisors
Important: as the main contractor, you are the one the inspectors look at. The attendance of your subcontractors and their people must also be registered correctly — read how responsibility for subcontractors works exactly.
What are the fines?
A missing or incorrect Checkinatwork registration is no small matter:
Up to €1,000
for a worker on site without a registration.
€600 to €6,000 per person
for the employer or contractor who does not provide a registration system.
Up to €36,000 and a possible prison sentence
in the event of a workplace accident without a correct registration.
What changes from 2027?
On 1 April 2027, CIAW gets stricter. Checking out becomes mandatory (hence the term Check In and Out at Work, CIAOW), registration must happen in real time on site and every worker registers themselves — on arrival and on departure.
Site registration, attendance registration and CIAW: the same thing
Site registration and construction site attendance registration are different words for exactly the same thing: electronically keeping track of who is present on site and reporting it to the NSSO through Checkinatwork (CIAW). Whether you call it site registration, site notification or CIAW — the obligation is the same, and from 2027 the mandatory check-out is added.
Checkinatwork with a QR code
A CIAW QR code at the site entrance is the simplest backup for registering someone without a smartphone or with a flat battery: one scan and the attendance is recorded. With AutoCheckIn, every site comes with a printable QR poster — it works alongside the automatic registration, not instead of it.
Frequently asked questions about Checkinatwork
What is Checkinatwork?
Checkinatwork (CIAW) is the mandatory electronic attendance registration of the NSSO (RSZ/ONSS) on large construction sites. Everyone working on the site is registered, so the authorities know who is present. It has existed since April 2014.
What does the abbreviation CIAW stand for?
CIAW stands for CheckInAtWork. You will also see CAW or, from 2027, CIAOW (Check In and Out at Work), because checking out then becomes mandatory too.
Who does Checkinatwork apply to?
Everyone actively working on the site: employees, self-employed workers, subcontractors, safety coordinators and site managers. As the main contractor, you are responsible for making sure everyone on your site is registered.
From what amount is Checkinatwork mandatory?
On construction sites with a total value of €500,000 or more (excl. VAT). If your site is above that threshold, the registration requirement applies to everyone working on it.
What changes in 2027?
From 1 April 2027, checking out becomes mandatory as well as checking in, everything has to happen in real time on site and every worker registers themselves. Registering in advance will no longer be allowed.
What is a CIAW number?
Every Checkinatwork registration comes with a unique registration number — sometimes called a 'CIAW number' — that proves the attendance has been reported. During an inspection, it shows in black and white that someone is in order. AutoCheckIn stores that number with every check-in and check-out.
What is the difference between Checkinatwork and Limosa?
Limosa is the prior notification for foreign employers and self-employed workers who come to work in Belgium temporarily. Checkinatwork (CIAW) is the attendance registration on the site itself. They are two separate obligations: a Limosa notification does not replace the CIAW registration.
Which app do you use for Check In at Work?
AutoCheckIn registers attendance on site automatically: your workers check in and out by themselves based on their location, without touching anything. They sign in once with their mobile number — no password, no training. That way you are ready straight away for the stricter check-in and check-out requirement of 2027.
Read more
The questions we get asked most often, each with its own page:
- Signing in to CheckinatworkWhere do you sign in with the NSSO, and what if it doesn't work?
- From what amount is it mandatory?The €500,000 threshold, the exceptions and when the obligation ends.
- Declaration of works or Checkinatwork?Two separate obligations — and why you need the site number.
- Adding a subcontractorWho registers whom, and what you are liable for as the main contractor.
- Check In and Out at Work 2027What changes: check-out, real time and the worker themselves.
- Time tracking in constructionGet exact hours from the mandatory registration — without paper timesheets.