Can a tag arm and disarm an alarm?
Arming, reasonably. Disarming, not on a tag alone, because a tag on a wall holds public content that anyone reaching it can read, and a tag is not a credential. The asymmetry between the two directions is the whole answer.
The two directions are not equal
Arming an alarm is a safe action. The worst outcome of an unauthorised arming is inconvenience.
Disarming is the opposite. It is the whole point of the system, and anything that can trigger it is a key.
So a tag by the door that arms on the way out is a reasonable convenience, and the same tag disarming on the way in is a different proposition entirely.
Designing them as one symmetrical automation is the mistake to avoid.
Why a tag cannot disarm safely
A tag holds content anybody can read with an ordinary phone, from a few centimetres, silently.
If the address on it disarms the alarm, then reading the tag is obtaining the means to disarm it, and reaching the tag is the only barrier.
A tag is not a credential: it asserts rather than proves, and it cannot resist being copied because reading it is copying it.
Locking the tag does not help, since locking prevents writing rather than reading.
What is reasonable
Arming from a tag by the door, which saves opening an application while carrying things.
A tag that opens the alarm application rather than performing an action, so the disarming still requires whatever the application requires.
A tag as one factor among two, where the system asks for something else as well. That is a design your alarm system either supports or does not.
And a tag inside the protected area rather than in a hallway anyone reaches, which reduces the exposure without changing the mechanism.
And what happens in an outage
Many home systems route commands through a service on the internet, so an outage can leave you unable to disarm from a phone at all.
That is a serious failure mode for an alarm and it is worth testing deliberately rather than discovering.
Keep the manufacturer's own keypad or fob working, whatever automation you add.
An alarm is one of the few places in a home where convenience should lose to reliability, and where a tag belongs alongside the proper control rather than instead of it.
Frequently asked questions
Can a tag disarm my alarm?
Technically it can be arranged, and it should not be on a tag alone. Reading the tag is obtaining the means, and a tag cannot prove anything.
Is arming from a tag safe?
Reasonably. The worst outcome of an unauthorised arming is inconvenience, which is not true of disarming.
Does locking the tag help?
No. Locking prevents writing and does nothing about reading, which is the exposure here.
What if the internet is down?
Many systems route commands through a service, so test it deliberately and keep the manufacturer's own keypad or fob working.