Signal Radar: Caught between flickers — we built it for that moment

Hey Hunters 👋 I'm Cheng, a solo indie developer. Signal Radar started with a problem I couldn't stop thinking about. THE PROBLEM NOBODY DESCRIBES PROPERLY If you've hiked deep, you know how signal behaves in the backcountry — it doesn't gracefully reappear when you wander back into coverage. It flickers. Half a second of one bar, gone, ninety seconds later a single second and a half, gone again. By the time you notice it on the lock screen and unlock with frozen fingers, the window has already closed. Every "emergency SOS" app I tried assumed you'd manually press a button at exactly that fleeting moment. Which is the same as assuming you can catch a firefly with chopsticks while wearing mittens. I built Signal Radar to do that catching for you. WHAT IT ACTUALLY DOES It runs silent in the background, 24/7, scanning cellular for the tiniest reconnect — even a 200-millisecond flicker. The instant signal returns, a pre-composed email fires: GPS coordinates, altitude, timestamp, your custom message. Pre-loaded into your trusted contacts. Locked screen, exhausted, even unconscious — it doesn't care. It's already done its job. And while you wait for that window, you're not helpless. I packed Gemma 4 (Google's on-device LLM) into the app. Photograph a snake — it identifies one of 50 venomous species worldwide and walks you through first aid. Photograph a sting — 40 bees/scorpions/spiders/marine toxins. Type "deep cut on thigh" — it explains pressure points, tourniquet thresholds, when to release. CPR, hypothermia, lightning, burns, drowning, getting lost — every survival scenario, illustrated, step-by-step. 100% on-device. Zero internet required. ON $4.99 AND THE PROMISE I priced it modestly because survival apps shouldn't be free-with-dark-patterns and shouldn't bleed you with subscriptions either. Pay once, works forever, no telemetry, no upsell. But here's what I want to say to anyone considering it: I genuinely, sincerely hope this app sits unused on your phone for the next twenty years. I hope you take it on your trip and the worst that happens is you forget you have it. I hope it never gets to fire its SOS. I hope you never need to ask the AI what to do about the snake bite, because there's no snake. I hope the only person who ever opens it again is the person you give the phone to. But if the day comes — the night your foot slides off the trail, the moment the dust storm rolls in, the second your boat takes water — I built Signal Radar to be the one light still on. The one tool that already did its work before you knew you needed it. TECH FOR THE CURIOUS - Flutter + flutter_gemma (LiteRT-LM iOS) for on-device LLM - Gemma 4 E2B (~2GB, runs on iPhone 12+) - Apple Vision feature print + classification for the two-stage image ID pipeline - Cloudflare R2 for emergency-number OTA updates (not user data) - Cellular polling via CTRadioAccessTechnology + signal-strength monitoring - 100% on-device — no backend, no analytics, no chat logs AMA on any of it — happy to talk about LiteRT-LM iOS quirks, how I tuned a 2B model to never invent phone numbers, the cc:948 vision encoder cold-start bug that took me three weeks, or anything else. And if you ever do need it — I hope it's the most useful $4.99 you ever spent. — Cheng