Why does the same tag trigger twice?
Because leaving and returning to the field counts as two taps. A hand that lifts slightly and settles again has presented the tag twice without intending to, and the phone has no way to know the second was not deliberate.
Leaving the field is the trigger
A phone treats a tag as newly present when it appears in the field. It does not remember that the same tag was there a second ago and decide you meant one tap.
So the sequence that produces a double trigger is: present, read, drift out of range, drift back, read again.
The movement involved can be tiny. A hand relaxing, a phone settling on a surface, a slight tilt at the edge of the working distance.
At the edge of range this is easiest, because a millimetre is enough to cross in and out.
Where it happens
A tag on a desk with the phone put down on it. The phone settles, rocks slightly, and reads twice.
A tag in a phone case or a wallet, which comes in and out of range as the object is handled.
A tag at the limit of the working distance, where the smallest movement crosses the threshold.
And a tag on a mount or cradle, where placing the phone involves a small amount of settling.
When it is worse than annoying
A tag that opens a page twice leaves two tabs, which is untidy and harmless.
A tag that starts an action with a side effect is different. Anything that increments, records, sends or toggles will do it twice, and a toggle run twice is back where it started.
That last case is the one that produces genuine confusion: a tag that appears to do nothing, because it did the thing and then undid it.
Where an action has consequences, the receiving side should tolerate a repeat rather than assuming one tap means one event.
Avoiding it
Move the phone away decisively after a read rather than letting it hover.
Position tags so that a phone is not left resting on them. A tag under a spot where people put their phone down will be read repeatedly all day.
Give the tag enough margin that small movements do not cross the threshold, which means a larger tag or a better surface.
And where the action matters, handle repeats on the server. A page that can be opened twice safely is easier to build than a tap that can only happen once.
Frequently asked questions
Is my tag faulty?
No. Being read twice is correct behaviour for a tag presented twice, and the second presentation was accidental.
Why does my toggle end up unchanged?
Because it ran twice and returned to its starting state. That is the clearest sign of a double trigger.
Can I stop the phone reading twice?
Not through a setting. Move away decisively, place tags where phones are not rested, and design the receiving side to tolerate repeats.
Does this happen on both platforms?
Yes, since it follows from the tag leaving and re entering the field rather than from any platform behaviour.