What fails is the logging, not the habit
The route to the app is often longer than the habit itself.
Opening the app is the real hurdle
Unlock, find the app, find the right habit, log it. Five steps for something that took two seconds. With ADHD that route is exactly where it breaks off.
At the pill box you think about the pill
Not about the app. That comes to mind three hours later, when you can no longer remember whether you took it.
Logging afterwards is guessing, not tracking
Filling in the evening from memory produces data you do not trust yourself. And it feels like homework.
An object that stands for one habit
The anchor sits where the habit already takes place. It does not remind you. It is simply there.
NFC stickers, written by the app itself
Name the sticker and decide what a tap logs. Then hold your iPhone against it and the app writes the link. NTAG213 or larger is enough, which is what the ordinary ten-packs are.
QR codes to print
Full page, or a grid at 3 × 3 and 5 × 5 cm, optionally with the habit name under each code. Cut out, stick on, done.
A fixed value, or a question
An anchor can log a fixed intensity or ask how it went when you tap. The pill was taken or it was not. Exercise comes in degrees.
Use codes that already exist
The barcode on the pill packet, your gym card, a conference badge. Scan it once, tie it to a habit, and from then on it counts.
What a tap actually does
The sticker carries an ordinary web address, not an app-only token. iOS shows a notification when you tap it, you tap that, and the check-in is in. That is one step more than you would expect, and I cannot change it: background sticker reads work no other way on iOS. To lose the notification you set up a Shortcuts automation once. The app walks you through the five steps, but only a person is allowed to create it.
What an anchor cannot do
It does not do the thing for you. The letter still has to be opened, the pill still has to be taken. An anchor only shortens the distance between doing and logging to a single touch. And it needs an iPhone that reads NFC in the background, so an iPhone XS or newer. Older phones, and anyone who would rather not stick anything anywhere, use the QR code or keep logging in the app.
The sticker belongs to you, not to the app
I deliberately do not lock the stickers the app writes. Locking is a one-way door on an object you paid for: no other habit could ever go on it, and one mistyped value turns it into rubbish. You can rewrite any sticker at any time, with another app too. And because it carries a real web address, tapping it on an Android phone, or an iPhone without the app, still leads to a page that explains what it is.
An anchor gives nothing away
The sticker holds an identifier for one habit and nothing else. No name, no data, no account. What you log stays on your device, and nobody learns when you were at your pill box.