Is this really super-scalable?

Yes. We could sell these things for <$50.

How many people would buy a dedicated gesture-detecting device?

More than 1/100 people. We have done market research.

Would it be better to write software for a device like a Fitbit or Apple Watch, which millions of people already own?

Surprisingly, the answer is no. The Apple Watch (last time we checked) didn't support this kind of software. But more importantly, most of our potential customers own no smartwatches or Fitbits at all. Also, the smartwrist ecosystem is fragmented so we'd have to write new apps for every different model and update them whenever the manufacturer changes something.

In our trichotillomania project, we first tried putting software on others' devices. It was a disaster. When we started making our own wearables everything just worked.

Wouldn't people learn to ignore the notifications over time? If I put a post-it note on my fridge saying "stop snacking!", that might cause me to think twice a few times, but eventually I might just start ignoring the post-it.

Our experience talking to people and selling similar devices for trichotillomania suggests the answer is close enough to "no" to make our device worthwhile.

Even if wearing the device was 100% effective at eliminating unconscious snacking, would this make a dent in obesity? Wouldn't people just get hungrier and then eat more at meals?

The device also counts how many bites you take during a meal. Users would have to change what they eat or how much they eat per bite in order to hack Snackwatch's metric.

If I did [set up a separate substack / wordpress / whatever], I would probably wind up cross-posting to lesswrong anyway, and the end result would just be a split-up comment section and more hassle posting and editing, with no appreciable upside, it seems to me.

This is exactly why I post on Less Wrong and then link to it from my personal website instead of crossposting. I wrote a program that crawls Less Wrong and then generates links on my personal website.

I especially like how reliably the Less Wrong moderation team prevents spam in the comments. Spam was a chronic annoyance when I ran my own comments section.