My tag stopped working after a while
Reading wears nothing, so a tag that worked and stopped has had something change. Either the tag was physically damaged, or its surroundings changed, or the tag is fine and the address it holds now leads somewhere that no longer exists.
It did not wear out
Reading a tag powers it and asks it to recite what it holds. Nothing is written and nothing is consumed, so a tag read a million times is electrically identical to one read once.
This matters because it removes the intuitive explanation. Heavy use is not the cause, which means something else changed and it is worth finding.
Data retention is not the cause either. Published figures far exceed the life of any deployment.
Physical damage
A crease across the antenna breaks the loop and kills the tag outright. Nothing is visible afterwards.
Repeated flexing fatigues the bond between chip and antenna, which produces an intermittent tag before a dead one.
Moisture destroys the substrate rather than the electronics. Paper swells, the adhesive releases, the antenna is free to deform, and the tag fails mechanically.
Heat and sunlight degrade the substrate and the adhesive over months, particularly on a surface in direct sun.
Confirm by testing a known good tag in the same place. If the good one reads, the installed tag is damaged.
The surroundings changed
A metal fixture installed nearby. A sign or a poster placed over the tag. A second tag applied on top of the first, which is more common than it sounds during a refresh.
A wireless charger placed on the other side of the surface. A shelf restocked with something conductive against the back panel.
These change nothing about the tag and everything about whether it reads. Look at the environment before condemning the tag, especially if several tags in one area failed at the same time.
Several tags failing together is almost never several tags failing. It is something that changed around them.
The tag is fine and the destination moved
This is the case people investigate last and should investigate first, because it costs nothing to check.
The tag holds a web address. The address still reads perfectly. The page it points to has moved, been deleted, or now returns an error.
From a user's point of view the tag stopped working. From the tag's point of view nothing happened at all.
Read the tag, copy the address, and open it in a browser. If it fails there, the fix is on your server and no tag needs touching.
This is also the strongest argument for putting a redirect address you control on the tag rather than a direct link, since a moved destination then becomes a change you make in one place.
Frequently asked questions
Can a tag be worn out by heavy reading?
No. Reads do not modify memory, so a heavily used tag is electrically unchanged. Look for damage or a change in the surroundings instead.
Several of my tags failed at once. Is that a bad batch?
Possible, and far more often something changed around them. Simultaneous failure across an area points at the environment.
How do I confirm the tag rather than the phone?
Test a known good tag in the same place with the same phone. If it reads, the installed tag is the problem.
Should I check the URL first?
Yes, because it costs nothing. A dead destination looks exactly like a dead tag to whoever tapped it.