QR codes on construction sites,
and what a scan is actually worth.

A QR code costs nothing to print and takes about three seconds to scan, which is exactly why it gets oversold. The code is the easy part. Whether the record it produces survives a payroll query, a client audit or a solicitor's letter eighteen months later is the part nobody demonstrates, and it has almost nothing to do with the code itself. What follows is what QR codes in construction are actually used for, what construction QR codes can and cannot prove, and where the idea runs out.

What the code actually is

A QR code is a two dimensional barcode. On a construction site it is normally printed on an A4 poster, laminated, and fixed to the site board or the cabin door. It holds a short string of data and nothing else. It is not a database, it does not know who you are, and it cannot record anything on its own.

That last point matters more than it sounds, because it decides how the whole arrangement behaves. There are two ways to build a site scanning system, and they are not equivalent.

The first is to make the code a web address. Point any phone camera at it and a page opens. This is the cheap version, and it is the one that produces the awkward conversation later, because a web address can be photographed and sent to somebody sitting at home. Nothing about the code distinguishes the person holding the phone from the person who was meant to be at the gate.

The second is to make the code meaningless to anything except your own app. A phone camera pointed at it opens nothing at all. The app resolves the code, and only for somebody already signed in as themselves. The identity comes from the login rather than from the poster, and the poster becomes what it should be: a way of saying which site, and nothing more.

The question worth asking any supplier is not whether the code is secure. Codes are not secure or insecure. It is what happens when somebody photographs the poster and sends it to a mate.

What a scan should record

A scan is worth having to the extent that it produces evidence somebody else will accept. Four things do most of that work, and a system missing any of them is producing an attendance note rather than a record.

• Who, established by the login. Not typed at the gate, not selected from a dropdown of names. The person is whoever signed into the app, which is why the app half matters as much as the code half.
• When, written by the server. A time read from the handset is a time the handset can change. Moving the clock forty minutes is not a sophisticated attack. A timestamp written server side cannot be back-dated from the phone.
• Where, checked at clock-in. The scan is accepted only inside the site’s geofence, a radius of 100 metres or less set per site, and the location is stored against the record for whoever approves it. That is enforcement as well as evidence, and its limit is covered below.
• Which job, decided by the poster. This is the one people underrate. If the code carries the site, sub-site or plot, then the hour is attributed the moment it is recorded, rather than allocated from memory on a Friday afternoon.

A photograph taken at the moment of clock-in sits alongside those. It is the cheapest form of proof available and the one that does most to change behaviour, because a face against a record is harder to argue with than a tick in a book.

How QR code clock-in works on a construction site, step by step

1. The office adds the site. The platform generates a numbered QR code poster for that scan point, in the firm's own branding. One per site, or one per plot or floor if that is the level you cost at.
2. Print, laminate, fix. A4, on the site board, the cabin door or the plot entrance, wherever the team already passes. That is the whole of the installation.
3. The operative opens the firm's own app. Signed in once with an email address and a password, then a four digit PIN every time after that. A phone camera on its own opens nothing, because the code is not a web address.
4. Scan, photograph, confirm. About three seconds. The app asks for a photograph at the moment of clock-in, and the office sees the clock-in at the same instant the operative sees the confirm screen.
5. The server writes the record. The time comes from the server rather than the handset, so a changed phone clock changes nothing. The location is checked against the site’s geofence, 100 metres or tighter, and a scan from outside it is refused. The location and the IP address of an accepted clock-in are stored against it and shown to the approver.
6. The hour lands on the job. The site, plot or floor comes from the poster that was scanned, so the hour is attributed before anybody types anything, at that person's rate for the day. Scanning again at the end of the shift clocks them out, and the site manager approves the week on the phone rather than deciphering it on a Friday.

Where the posters go, and how many

The number of scan points is a costing decision dressed up as a logistics decision, and it is worth taking deliberately.

One code for the whole site is the simplest thing to run. Every hour lands on the site, and if the site is the level at which you cost work, that is the right answer and there is nothing more to think about.

One code per plot, floor or sub-site changes what your job costing can tell you. A housebuilder with a poster on each plot gets labour cost per plot as a matter of record rather than apportionment. A fit-out contractor working three floors of the same building gets three costed rows instead of one lump. The cost of that precision is a handful of extra laminated posters.

Where the poster physically goes is a more practical question, and the answer is wherever the team already passes. On a housing site that is usually the plot entrance. On spread out groundworks with no gate to speak of, it is the cabin. In a building it can be the lift lobby on each floor. A scan point that requires a detour will be resented within a fortnight and worked around within three.

How to make a QR code for a construction site

There are two ways, and choosing between them is the whole decision.

For anything that only has to open a page, a drawing set, a link on the hoarding, a feedback form, any free generator will make a code in two minutes. Paste the address, download the image, print it. Use an address you control, so the poster survives the page moving.

For clocking in, do not make the code yourself. The code has to be resolved by the system that will write the record, so the poster comes out of that system, numbered for each scan point, and means nothing to a phone camera. In Unibuild it is printed from the office side of the platform with your firm's name on it, one for the site or one per floor or plot, and that is the whole of the setup on the poster side.

Printing is the same either way. A4, laminated, matt rather than gloss because glare defeats a camera, fixed at chest height where people already stop, and replaced when it is scuffed. A code that has to be read from a lorry cab wants to be bigger than one on a cabin door.

What stops somebody scanning for a mate

Nothing stops it. Anybody who tells you otherwise is selling something. What a well built system does is raise the cost of it until it is more trouble than turning up, and it is worth being precise about how, because the individual measures are weak and the combination is not.

1. The photograph. Somebody clocking a colleague in has to produce a photograph at the moment of clock-in. That is where most casual attempts stop.
2. The login. If identity comes from a signed in app rather than the poster, the second person has to hand over their credentials rather than forward a link. That is a different kind of favour to ask.
3. The geofence. A scan from outside the site’s radius does not go through, so clocking a mate in from home fails before the photograph is even asked for. The location of an accepted clock-in is stored and visible to the approver.
4. The server timestamp. Removes the simplest correction of all, which is arriving late and adjusting the phone clock.

Put together, clocking in for a mate stops being a thirty second favour and becomes a deliberate act involving somebody else's login, a photograph and being on site. That is a real deterrent and an honest claim. It is not prevention.

Pros and cons of QR codes on a construction site

The case for. No turnstile, reader or wiring at the gate, and a poster that is replaced from a printer and a laminator. A scan from outside the site’s geofence is refused. The time is written by the server, not by the person claiming it. The hour is attributed to the job the moment it is recorded. The record is held against the person and the project, so it outlives the cabin. It runs on the phone the operative already carries, through the firm's own app on iOS or Android.

The case against. It needs that app installed and a signed-in user, so the first fortnight is a rollout rather than a print job. A scan proves presence, not work. It deters scanning for a mate rather than preventing it. And a code that is only a web address proves almost nothing, which is the version most of the cheap arrangements turn out to be.

What a QR code cannot do

Three limits are worth knowing before anybody signs anything, because all three tend to surface after the decision rather than before.

A geofence proves where the phone was, not what the person did. Unibuild checks every scan against a radius around the site, 100 metres or less, set per site, and a scan from outside it is refused. That closes the scan-from-home problem. It does not prove that the person inside the fence then worked, and it will refuse a genuine scan from the lay-by beyond the fence, which is why the radius is set to the site rather than the postcode, why the poster goes where the team already passes, and why the office can still enter a clock-in with a manual flag when there is a reason.

A scan proves presence, not work. It records that a person was at a scan point at a time. It says nothing about what they did afterwards, and any supplier implying otherwise is describing surveillance rather than time recording.

It does not fix the rollout. This is the one that actually decides whether a system works. The paper route has to be closed on a named date, and supervisors have to expect the scan for the first fortnight and say so. Where field rollouts fail, they fail in about week three, for reasons that have very little to do with the software. That pattern is set out in why field app rollouts stall in week three.

Keeping the record, and for how long

Time records are not only a payroll convenience. CDM 2015 makes the principal contractor responsible for inductions and for keeping unauthorised people off the site, without saying how either is evidenced. The Working Time Regulations 1998 require employers to keep adequate records to show whether the weekly working time limit is being complied with, and HMRC expects payroll records to be kept for three years from the end of the tax year they relate to. A civil claim can arrive considerably later than either.

That is the practical case against a signing in book in a cabin. The book is accurate and complete right up to the day the cabin is demobilised, which is also the day it stops being findable. A record held against the person and the project outlives the site, and outliving the site is the entire point.

What QR codes are used for on construction sites

Most of what is written about QR codes in construction is a list of things a code can open, and the lists are long. What they hide is the split that matters. Some uses only need a code that opens a page, and any free generator will make one in two minutes. Others need the scan to prove who did it, and those only work when the code is resolved by an app the person has already signed into. The ten uses of QR codes for construction sites below are the ones that turn up on UK jobs, with the ones that need a signed-in app first.

1. Clocking in at the gate. The operative opens the firm's own app, scans the poster, takes the photograph it asks for, and the server writes the time. This is the use the rest of this article is about. How the hour then lands on the job is on the construction timesheet software page.
2. Who is on site now. The same clock-in is what a live view of every site is built from. The roll call at the muster point is a separate register, but it is only as good as the record of who came through the gate, and if that record is a book in the cabin, the roll call is in the cabin too. See who is on site now.
3. The RAMS for that trade, at the point of arrival. Because the scan already knows who has arrived and what trade they are, it can put the method statement for that trade on that job in front of them before they start work, and record the signature against the version they read. See RAMS signed at the gate.
4. Labels on tools, plant and assets. A label on a breaker, a transformer or a genny that opens the item's own record on the phone: PAT result, service history, attachments, who has it. Nobody uses a tool that is out of date because the date is on the thing. See assets and inventory.
5. Labels on fire doors. Each door carries its own label, printed from the register with the door reference and the firm's name, so an inspection is recorded standing at the door rather than from a list in the cabin. See fire doors and fire assets.
6. Inductions. A code on the hoarding or the cabin door that opens the induction video or the booking form for a visitor. This proves that a page was opened, not who watched it, which is why the better arrangement is an induction completed before the person arrives and recorded against their name.
7. The current drawing. A code on the site board that opens the drawing set at its latest revision, so nobody is building from the copy in the van. Any document system with a stable address can do this.
8. Deliveries and stock. A code on the bay or the pallet that opens the delivery note or the bin, so what arrived and where it went is recorded at the gate rather than reconstructed from a pile of paper on a Friday.
9. Public information on the hoarding. Site rules, the emergency number, considerate constructors details, the programme for neighbours. A web address in a code is exactly right here, because the whole point is that anybody can open it.
10. Feedback and reporting. A code that opens a near-miss form, a snagging report or a neighbour complaint form. Useful, anonymous by design, and no use at all as evidence of who reported what.

The first five want the second kind of code, resolved only inside a signed-in app, because each of them is only worth having if the record says who. The last five want the first kind, a plain web address, because the whole point is that anyone can open it. Sites go wrong when they use the cheap kind for the first five and then wonder why the record will not stand up. In the United States the same gate poster is called a jobsite QR code, and the split is identical.

Where to start, on Monday

Pick a date three months ago and one site. Produce the list of who was on that site that day, with the times they arrived, and the job each hour was worked against. Time yourself doing it.

If the answer takes longer than a few minutes, or arrives as a photograph of a page in a book, the problem is not that you lack QR codes. It is that the record is being made somewhere other than where the work happens, and every argument you have later will start from a reconstruction rather than from evidence.