A dad feeding at midnight moved the feeding log to his iPhone Lock Screen

응앱2 is a baby-tracking app built in Korea by a first-time dad. No unlocking needed: tap the lock screen to start logging a feed, and your baby's face sits in the Dynamic Island. Launched Oct 12, it ranked in the top three of the Korean Medical Top Grossing chart most days over its first three weeks, yet has only 30 ratings. It isn't riding a new need or visible paid acquisition. It makes one interaction smoother than anyone else, and the developer posts lock-screen screenshots on Threads again and again. Anyone can copy this, but the category is crowded and the money is modest.

A Threads post with 41k views

On Oct 2026 26, the Threads account @minton__daddy ("민턴 아빠", Minton's dad) posted with two lock-screen screenshots:

Moms with iPhones, look at this. If you set your lock screen like this it's so cute 🐣🐣 I built this app during night feedings lol (아이폰 쓰는 육아맘들 이거봐봐 잠금화면 이렇게 해두면 넘 귀여워 🐣🐣 내가 새벽수유하며 만든 앱이야 ㅎㅎ)

His first reply was his own, just "앱은 여기!" (App's here!) with an App Store link. By 11-06, the post had 41k views, 144 likes and 31 replies (Threads, 11-06).

His bio reads: "Dad to a son born Jan 26 23, first-time developer dad, building the newborn tracker 'Eungapp' during night feedings." The posts don't read like ads. They use casual Korean banmal, the way a friend in a moms' group would share.

Four days after the post went up, ratings started climbing: from 10-30 onward, daily new ratings went from 1 to 3, 11-03 added 6 a day, 11-06 added 7 a day, rising from 10-28's 6 to 11-06's 30 (App Store Korea store, daily rating count).

What it is

An iPhone-only newborn tracker for feeds, diapers, sleep, height and weight, with timelines and charts. The store title spells out the pitch: "잠금화면 원클릭 수유기록" (one-tap feed logging from the lock screen).

Two things set it apart:

• Log from the lock screen. Lock-screen widgets and Live Activities have buttons. Tap once to start the timer. No unlocking, no hunting for the app. The store description says: "Fumbling to unlock and open the app while feeding is a hassle, right?"
• Your baby's face. Upload a photo and the app cuts out the baby's face and puts it on the lock screen and Dynamic Island.

Basics are free. Plus is ₩3,000 a month, ₩18,000 a year, or ₩28,000 lifetime, one purchase covering the whole family (App Store Korea, 11-06). Requires iOS 26 or later.

It's called "2" because the developer shipped a first-gen "응앱" in Mar 13, which built up 156 ratings. The second gen is a rewrite. Its description opens: "I built this for myself, and when so many people noticed, I made a sequel." Ships 25 days after launch, with the version moving from 2.1 to 2.7.0,11-06, which added "timer logging for pumping too."

How big it actually got

The numbers are small, and should be taken with a grain of salt.

The bar for the Korea Medical Top Grossing chart is low. Ranks 4 through 15 include apps for snoring logs, anatomy atlases and pharmacists' drug checks. Reaching the top three means it's getting steady in-app purchases every day, not that revenue is big. Based on 30 ratings, the user base is in the thousands. Daily revenue may be only tens to a hundred or two dollars (estimate; Apple doesn't publish it).

Part of the growth is users moving over from the old app. Of the 11-06 reviews visible before 21, over half say "I've used 응앱1 since..." The first gen's rating count stopped growing at 10-28 156, so many of the second gen's early ratings and purchases came from first-gen users.

Where users come from

First, the developer's own Threads, the main channel. The formula stays fixed: the same line "Moms with iPhones, look at this, set your lock screen like this and it's cute" with a few words swapped, repeated with lock-screen shots, and the link in the first reply. Before and after 11-03 he posted again, to 8,800 views. Not every post lands. Other posts on his profile with the same format got only one or two likes, and another post, "set it up before you give birth," listed four points (real parenting starts once you're home, couples taking shifts and scrambling, feed times forgotten if written on paper, and lock-screen logging plus family sharing), and got about a dozen likes. The 41k post was a lucky hit.

The first gen grew the same way. He wrote about it on Instagram @eung_app in Apr 1, and said that after "a light promo on Threads, views went past 50k." First-gen reviews include "Saw it on Threads and quietly downloaded" (3-20) and "Found 응앱 by chance on Threads" (9-14).

Second, first-gen users migrating. The second gen's description promises that "first-gen users can move their data and purchase records over (no need to buy again, of course)."

Third, store search (inferred). The title includes the search term "수유기록" (feed log). Searching it in App Store Korea, the app ranks #3, behind BabyTime and 삐요로그. The first gen's subtitle even read "빠르고 편한 베이비타임 기록" (quick, easy BabyTime-style logging), riding the leader's name.

Not found: paid ads (not found doesn't mean none were run), discussion on X, press coverage, TikTok.

Why users pay

Three themes keep coming up in reviews.

One tap from the lock screen. "Other apps make you open them to log, which is inconvenient" (11-05); "It's so convenient because it works from the lock screen. I can't go back to other apps, and I paid for it" (11-01). One review compared it to incumbents: "There are lots of famous baby trackers, but the input and viewing aren't intuitive. After trying them all I settled on 응앱, even grandparents can use it" (10-31).

The baby's face is cute. "You can decorate the lock screen and Dynamic Island with your baby's photo, I love it" (11-01). This is also why the Threads posts spread: they sell "so cute," not features.

Family sharing, the paywall. With a newborn, two people take shifts and need to know when the last feed was. "We don't have a home camera, but I can share the app with my husband, and he can see the baby's status in real time while at work" (11-04); "I bought the lifetime plan, worth it" (10-31).

The second gen also added baby-food tracking (이유식, frozen food-cube management). The timing works: the babies from the first gen's March launch are now six or seven months old and starting solids. "Right when we started solids in December, 응앱2 added this, it's great" (11-04); "I was going to switch to another app since there was no baby-food mode" (10-31). The product grew up with its users' kids, so existing users have no reason to leave.

The complaints cluster in two places. No Android support: "My husband uses a Galaxy, can't we share?" (10-28), "When's it coming to Play Store? My husband has a Galaxy" (10-27). First and second gen split apart: "Why is it a separate app from the same one?" (1 stars, 10-17), "I was charged twice" (10-30), "I bought first-gen Plus and the second gen says there's no such account" (10-28).

Who it's competing with

Korea's category has both old giants and this year's wave of indie developers crowding in. 응앱 didn't take off because "nobody is doing this". It took off by doing one interaction point best and putting it in the app name. The moat is shallow: BabyTime already has lock-screen widgets, and turning "display" into "tappable" is just one update away.

If it were you

Verdict: This is an example of a crowded category broken open by "one interaction point + a real persona + one screenshot-worthy asset." The playbook can be copied, but copying it in Korea doesn't make sense, and the revenue ceiling is low. What's worth doing is taking it to another market, or building the Android version it skipped.

Who it's for: indie developers who are raising a child now and can write iOS (or Android). For the year around birth, the persona is real, you are the user, and you can read the requests in the comments right away.

Who it's not for: teams that want big revenue; people with no kids who would have to fake the persona (it shows immediately); anyone counting on organic App Store traffic, since names like BabyTime and Huckleberry own the search terms.

How to build it: track only, and deliberately keep it small. The first screen is the lock-screen widget and Live Activity, with one tap to start the timer. The baby's face in the Dynamic Island is both a feature and ad creative. Paywall only on family sharing: one purchase covers the family, with a lifetime one-time option. Add baby food and pumping only when your own kid needs them. Two ways to copy it: take it to a language and market where nobody does this yet (Japan, Taiwan and the US all work, and you can check for similar apps by searching "lock screen feeding" in the store), or build an Android version for Korea that works with iPhone, catching the people whose husband uses a Galaxy.

How to get users: follow his rhythm. On Threads (or wherever moms gather in your market, such as RedNote or Instagram), post lock-screen screenshots in a real-parent voice, with a line like "I built this during night feedings," and put the link in the first reply. Repeat the same format every few days with different words. Most posts get a few likes, and one hit is enough. Scenarios like postpartum-center stays or hospital-bag checklists, "set it up before you give birth," are also worth writing about.

How long before it's gone: one-tap lock-screen logging is a point an incumbent can add at any time. Once BabyTime makes its lock-screen widget tappable, the trick stops working in Korea. The same goes for other markets, so move before the local leader updates. Based on how big companies ship, you probably have about half a year (inferred).

What it means if you misread it: ① By early next year, 응앱2's rating count stalls under 200 and its Top Grossing rank slips out of the top 10 in Medical: that means it lives off a first wave of old users and one viral post, and new users aren't coming in; ② if 베이비타임 or PiyoLog ship a tappable lock screen button and 응앱's rating growth doesn't change: that means people are buying the persona and the design, not just the interaction, so followers have a harder time copying it; ③ you copy the playbook in another market, post twenty times, and not one post passes 10K views: that means the approach depends on Korea's parenting community on Threads.