NFC Tags: Reading, Writing & Best Practice

Answer first

An NFC tag is a coin- or sticker-sized chip with no battery. Hold a phone within about 1–4 cm and the phone powers it, reads what is stored on it and acts on it — opens a link, starts a call, shows a menu. Writing is free: any phone with NFC and a free app (NFC Tools on iPhone and Android) can put a link, a phone number or an SMS on a tag in seconds, and rewrite it later unless you lock it. The one rule that trips everyone up: phones only react automatically to link-type records. A plain text sentence sits silently on the chip until someone opens a reader app.

How a tap works

• Passive chip, no battery. The phone's radio powers the tag for the split second it is over it. Nothing to charge, nothing to wear out.
• Range 1–4 cm, so a tag only fires on purpose. Sealed inside 1–3 mm of PLA it still reads fine — our pet tags have the chip sealed mid-print under 1.2 mm each side, our logo plaques read through 2.6 mm.
• iPhone: iPhone XS/XR and newer read tags in the background — hold the top edge of the phone near the tag and a banner appears. iPhone 7–X need the NFC Tools app open (or a Shortcut). Android: nearly every phone since 2015 reads in the background; the sweet spot is usually the middle of the back.
• Metal kills it. A tag directly on steel or aluminium will not read. Keep 3 mm+ of plastic, wood or air between the chip and any metal, or buy "on-metal" tags with a ferrite backing.

Chips: which one to buy

All three are ISO 14443-A, work with every phone, and cost cents each in packs of 25–100 (~A$0.40 per sticker). Avoid "Mifare Classic" tags — iPhones ignore them.

What to write on a tag (record types) — what the phone actually does

Writing a tag — 60 seconds, free

1. Install NFC Tools (free, iPhone and Android). Android alternative: NXP TagWriter.
2. Write → Add a record → pick URL, Phone number or SMS → type it → Write → hold the tag to the phone until it confirms.
3. Tap it with a second phone to check the banner appears. If it does not, the record type is wrong (see the table) or the tag is on metal.
4. Lock only when you are sure. "Lock tag" is permanent — nobody can rewrite it, including you. For pet tags and bag tags leave it unlocked so you can change the number; lock plaques in public places so a prankster cannot repoint them.
5. Batches: NFC Tools has Write / Batch (same record to many tags one after another). We program every chip we ship, so for our products you only do this when you want to change something.

Best practice by scenario

Restaurants & cafés — table plaques, counter plaque

• One plaque per table pointing at the menu or ordering page; add ?table=12 (or a UTM) so you can see which tables are used.
• A counter plaque for reviews: link straight to your Google review page (the "write a review" short link), not the business profile — one tap, one step.
• Lock these tags; they are in public. Put the plaque on wood, laminate or glass, never straight on a steel bar top (or use the standoff holes).
• Print the URL under the logo in tiny text as the fallback for phones with NFC off.
• Rewritable means seasonal: same plaque, new menu link every season.

Pet tags

• Write a phone number (tel:), not a sentence: a finder's phone shows "Call 0412 …" instantly, on any phone, with no app and nothing that depends on a website being up.
• Keep the engraved name and number on the tag as well — NFC is the second layer, not the only one.
• Never put your home address on a pet tag (NFC or engraved). Phone + suburb is plenty.
• Leave the chip unlocked so a new number or a new owner is a 20-second rewrite.
• Ours: the chip is sealed inside the tag mid-print — nothing to peel off, waterproof, reads through the plastic. We program your number before shipping, or pick your own option.

Kids' bag & lunchbox tags

• SMS to a parent is the right record: a teacher or bus driver can text "found Ollie's bag at gate 2" without a phone call to a stranger.
• First name only on the outside; the phone number lives on the chip. Don't write the school or the child's surname where a stranger can read it.
• Add an sms: with a pre-filled body: sms:0412345678?body=I%20found%20this%20bag — the finder just presses send.
• Daycare rule: tags on bags and drink bottles, not on the child.

Luggage & key rings

• Key ring: tel: to you, plus a "reward for return" line engraved.
• Luggage: mailto: or tel: and your destination hotel in the engraving — never the home address (an empty house is the risk).

Household items

• Guest Wi-Fi tag by the router: Wi-Fi record for Android, plus a link to a page with the password for iPhones (or an iPhone Shortcut that joins the network).
• Appliance & tool manuals: a tag on the dishwasher, the mower, the printer → link to the PDF manual or the spare-parts page. Ends the "where is the manual" search.
• Plant care: tag in each pot → link to the care sheet (light, water, feed). Our knit-stack and fluted planters take a 25 mm sticker on the base.
• Pantry & spice jars: link to the recipe or the reorder page; medication: link to the dosing sheet for carers.
• Storage boxes & tool drawers: tag on the lid → a shared note or sheet listing what's inside. Our box maker and slab boxes can have the pocket added.
• Family notes: a tag by the door → the shared shopping list or calendar.
• Anything you'd write on masking tape, write on a tag instead — it survives washing and never fades.

Home automation (no data on the tag needed)

• iPhone — Shortcuts app → Automation → NFC: scan a blank tag once, choose actions. Bedside tag = alarm on + lights off; front-door tag = "leaving" scene; car tag = start navigation + playlist; kitchen tag = 10-minute timer. Runs on the tag's serial number, so the same tag can still carry a link for guests.
• Android: NFC Tools Tasks (set Wi-Fi, volume, open an app), or Tasker for anything complex.
• Home Assistant: the companion app's Tags — scan → any automation (lights, vacuum, garage). Tags on the wall are cheaper and more reliable than smart buttons: no battery, no pairing.
• Put automation tags where the phone already is: bedside, desk, car mount, entry shelf. A printed plaque with a symbol beats a bare sticker.

Formada3D specifics

• Stock chips: 25 mm round NTAG213 and 21 × 11 mm rectangular NTAG213, included with any NFC option, programmed before shipping. Smaller chips on request.
• Pet ID Studio: chip sealed inside (printer pauses at layer 7, chip goes in, print closes over it). Choose "call my number", "text my number" or a web link at checkout; change it later with any NFC app.
• Logo plaques & tags: a Ø25.6 mm pocket in the back, sticker pressed in after printing; 2.6 mm of plate over it reads fine.
• Tags stay rewritable unless you lock them; we never lock unless you ask.

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