Technology
Using NFC tags to verify field staff were really on site
How do you prove a cleaning or inspection log was entered on site? We compare QR and NFC trust levels, explain tag writing and locking, and cover attendance.
The most reliable way to confirm that field staff were really at a location is to tie each log to evidence that can only be read at that exact spot. In EnaFeedback, that evidence comes from one of two sources: an NFC tag carrying a hidden trust token, or a live display QR code that changes every few seconds. A printed QR poster gives fast access, but on its own it can't prove presence, because anyone can photograph it and scan it from somewhere else. This post explains the difference, how tags are written and locked, and how all of this works for cleaning logs, inspection logs and attendance.
NFC verification needs the mobile app
NFC verification works only in the EnaFeedback mobile app. Reading a tag's trust token, writing and locking tags, and NFC-verified cleaning, inspection and attendance logs all run through the app. A phone that taps a tag without the app opens the location in the browser, which is an ordinary, unverified visit, the same as a QR scan. The app is in internal testing and coming soon to the App Store and Google Play.
Why "a log was entered" isn't the same as "someone was there"
Paper checklists have a well-known weakness: the place where the signature goes isn't necessarily the place where the work happened. The sheet on the door of the 2nd-floor restroom in Building B can be filled in all at once at the end of a shift. Going digital doesn't fix this by itself. A staff member can tap "Cleaning done" in an app from the far end of the hallway, or from the break room.
So the useful question for a digital cleaning log isn't "is there a log?" but "what evidence backs this log?" EnaFeedback attaches two flags to every cleaning log, inspection log and check-in or check-out:
- Verified: Did the location come from an NFC trust token or a live display QR?
- Fresh: Was the log written within 5 minutes of the scan?
Both flags show up in reports. Managers can look beyond the raw count and see how many logs are actually backed by on-site evidence.
QR vs. NFC: comparing trust levels
Every location has a unique 6-character code, and the printed QR, the live display and the NFC tag all point to the same location. What differs is the evidence that reaches the server at scan time.
| Entry point | How it works | Trust level | Best for |
|---|---|---|---|
| Printed QR poster | Fixed link, scanned with the phone camera | Unverified | Visitor feedback, hygiene ratings, surveys |
| Live display QR | The screen fetches a new code every 15 seconds; each code is valid for 30 seconds | Verified | Entrances, waiting areas, kiosks |
| NFC tag, read with the mobile app | The hidden trust token on the tag is checked by the server | Verified | Restrooms, hallways, plant rooms, field points |
| NFC tag, read with a browser | The link opens, but the trust token can't be read | Unverified | Quick access for visitors |
The last row matters. When a phone taps an NFC tag through the browser, it only opens the link. It can't read the separate trust record on the tag. A verified session requires reading the tag with the EnaFeedback mobile app. If the app is installed, tapping the tag opens it directly; if not, the regular web page opens.
How is the trust token stored?
The trust token written to an NFC tag is a 256-bit random value. The server never stores the token itself, only its SHA-256 hash, and compares it using a timing-safe check.
Writing, verifying and locking tags
NFC tags are written from the NFC settings menu in the EnaFeedback mobile app. There's no web-based tag writer, and only users with the Owner role can do it. The mobile app for Android and iOS is currently in internal testing and coming soon to the app stores.
There are three actions:
- Save: Writes the location link and a fresh trust token to the tag.
- Verify: Reads the tag back to confirm it points to the right location.
- Lock: Makes the tag permanently read-only. This can't be undone.
Locking stops anyone from overwriting the tag with a different link. That's why the recommended order is always save, verify, then lock. If you spot a mistake after locking, you'll need to replace the tag.
Field installation checklist
- Finish the location hierarchy (Building → Floor → Unit → Location) in the admin panel first.
- Don't stick tags directly onto metal; metal can weaken NFC reads. Use on-metal tags where needed.
- Mount tags where staff naturally pass, at a height visitors can't easily reach or peel off.
- Run Verify right after writing each tag, then lock it.
- Put a small location label next to the tag (for example, "Building B, 2nd floor, men's restroom"). It makes fault reports easier.
- Watch the verified-log rate in reports for the first few days. Points that stay low usually have badly placed tags.
Making verification mandatory: two settings
In the staff modules, two settings tighten proof of presence:
- Verification required: A log is accepted only if the location came from an NFC trust token or a live display QR. Sessions opened from a printed QR are rejected.
- Fresh session required: A log must be written within 5 minutes of the scan. Staff can't scan a tag and then log work half an hour later from somewhere else.
Prepare the site before you turn these on. Every location needs either a locked NFC tag or an online live display, and staff need the mobile app on their phones. Otherwise the team can't log work, and you lose both time and data.
There's also a 30-minute cooldown per person, per log type, per location. The same person can't enter two cleaning logs in a row for the same restroom, which keeps counts honest.
Cleaning and inspection logs in practice
Field staff have two roles: the Cleaning role enters cleaning logs and the Control role enters inspection logs. One person can hold both.
In an inspection log, the staff member ticks the control items an admin has defined (for example, "soap refilled," "floor dry," "bin emptied"). The system calculates a quality percentage as checked items divided by total items, and 70% or higher counts as sufficient. You can set an alert rule for inspections below 70%.
Work logs don't take photos. Proof of presence comes from the verified and fresh flags stored with each log, not from images. That keeps the extra effort for staff close to zero and avoids piling up pictures that might contain personal data.
Combine this with cleaning and inspection plans and the picture gets clear. The plan compliance screen compares expected and actual logs for every shift, and the verification settings show that those logs were really entered on site.
Attendance: the start and end of a shift
The same logic applies to staff check-in and check-out. At the start of a shift, a staff member scans a location to check in, and scans again to check out at the end. The system stores the location of both events and their verified and fresh flags separately.
A few rules to know:
- A person can have only one open session at a time.
- Checking out records the duration.
- If someone forgets to check out, they close the session themselves with I forgot to check out. These sessions are left out of duration stats, and the system never closes sessions automatically.
- You can set alert rules for check-in, check-out and forgotten check-out.
Reports show verified, fresh and forgotten rates per person, and you can export results to Excel or a PDF summary.
Questions to settle before rollout
| Question | Why it matters |
|---|---|
| Which locations will require proof? | Starting with critical areas is easier than switching the whole facility at once. |
| Do staff phones support NFC? | Verified NFC reads need the mobile app on an NFC-capable device. |
| Live display or NFC? | Displays need power and a network; NFC tags are passive and need no upkeep. |
| Who will write the tags? | Writing and locking are limited to the Owner role, so plan installation day around that. |
| How will you measure success? | Verified-log rate and plan compliance are two good starting metrics. |
FAQ
Can staff photograph a tag and scan it from somewhere else?
No. A photo of an NFC tag is useless; the trust token is read by the mobile app only when the phone is physically near the tag. A photo of a printed QR can be scanned, which is why printed-QR sessions count as unverified.
Can visitors use the same NFC tag?
Yes. When a visitor taps the tag, the location page opens in the browser and they can rate cleanliness or send feedback. That session isn't verified, but visitor actions don't need it to be.
Does NFC verification work without the app?
No. Browsers can't read the trust token on the tag, so NFC verification works only in the EnaFeedback mobile app. Tapping a tag with a phone that doesn't have the app opens the location in the browser with an unverified session, just like a printed QR.
Can I rewrite a locked tag?
No. Locking is permanent. If a location changes or a tag is damaged, write and lock a new one.
Can I get verified logs without NFC?
Yes. If the location has a live display, scanning its rotating QR also opens a verified session. The code refreshes every 15 seconds, and old codes expire shortly after.
The bottom line
Proof of presence is what makes your cleaning and inspection data trustworthy. NFC tags and live displays create that proof without extra work for staff, and the verification settings let you decide how strict to be. Learn more on the field app and cleaning tracking pages, or request a demo to try it in your own facility.