What is a tamper evident NFC tag?

How they work

The antenna is bonded to the surface more strongly than it is held together. Lifting the tag tears the conductor, which opens the loop.

An open loop collects no energy, so the removed tag is inert. There is no partial function and no way to reassemble it.

Some constructions also leave a visible mark on the tag or the surface, which gives a human check alongside the electronic one.

The mechanism is destructive by design, which means these tags are single use in a sense ordinary tags are not. A tag applied to the wrong spot is a wasted tag.

What it proves

That this physical tag is still where it was applied. A tag that reads has not been peeled off, because peeling it would have ended it.

That is a genuinely useful property. It closes the substitution attack where someone lifts a tag from one item and applies it to another, which is otherwise trivial.

Combined with a record of which identifier belongs at which location, it also lets you detect a tag that has been added rather than moved.

What it does not prove

That the content is authentic. Anyone can read the tag and write the same content to a blank one, then stick that blank one nearby. The copy works, and it is not tamper evident about anything.

That the item is genuine. The tag attests to itself, not to what it is attached to.

That nothing was covered. Placing a second tag over the first does not disturb the first at all, and a reader may answer to the new one.

Where authenticity genuinely matters, the mechanism is a chip that authenticates cryptographically, which proves to your server that it is the tag it claims to be. A copy holding identical content fails that check because it cannot produce the proof.

Using them properly

Record which identifier is at which location before deployment. Without that record, tamper evidence tells you a tag is present and nothing about whether it is the right one.

Apply once, carefully. The destructive mechanism means repositioning is not an option, so plan the placement before peeling the liner.

Check the surface. Tamper evidence relies on the bond to the surface being stronger than the tag, and a dusty or low energy surface breaks that assumption in the attacker's favour.

And decide what happens when a tag stops reading. Tamper evidence only helps if a missing response triggers something, so a deployment that never notices a dead tag has bought nothing.