I built an app that makes you solve math before you can start doomscrolling

I check my phone around 50 times a day. All that muscle memory built up just to doom scroll and waste time. I tried other screen time apps but there was hardly any friction.

Then I saw prayerlock (an app that makes you pray before unlocking apps) on the StarterStory podcast and it's making around $20K+ per month. Brilliant idea making the friction meaningful to the user.

As the creator of Apptato, a YouTube channel with 65K subscribers dedicated to brain games and mental math, the idea immediately hit me. What if the unlock ritual was solving mental math? You'd train your brain every time you reach for a distraction. Your phone addiction becomes your daily workout.

I built NumLock in about a month with AI assistance (Opus for spec, Sonnet in Xcode for coding). The core loop: choose which apps to block, solve 5 math problems to unlock them, apps stay unlocked for a grace period, then shields come back automatically.

Hardest part wasn't the math engine or the UI — it was grappling with Apple's Screen Time API. ShieldActionExtension silently refused to execute on device, DeviceActivitySchedule rejected any interval under 15 minutes, and UserDefaults failed inside extension sandboxes. I rebuilt the reshielding system three times before landing on a three-layer redundant architecture that actually works.

Final feature set: 25 levels of adaptive difficulty, 4 grace periods (15 min to all day), streak tracking with best streak records, and a clean stats dashboard. Fully on-device, no accounts, no data collection.

NumLock launched April 14, 2026 for $4.99/mo or $39.99/year with a 7-day free trial. Try it at numlock.app.

Would love feedback from anyone who's built screen time or habit apps — what worked, what didn't? Also curious if the math-as-friction concept resonates or feels too niche.