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Signal Radar
Caught between flickers — we built it for that moment
In the wild, signal doesn't return cleanly — it flickers for half a second, gone, returns ninety seconds later for a second and a half, gone again. You can't catch it. Signal Radar can. 24/7 background watch — the moment signal returns, GPS-SOS fires. Plus offline AI for snake bites, CPR, hypothermia. We hope you never need it.
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
About Signal Radar on Product Hunt
“Caught between flickers — we built it for that moment”
Signal Radar was submitted on Product Hunt and earned 5 upvotes and 1 comments, placing #94 on the daily leaderboard. In the wild, signal doesn't return cleanly — it flickers for half a second, gone, returns ninety seconds later for a second and a half, gone again. You can't catch it. Signal Radar can. 24/7 background watch — the moment signal returns, GPS-SOS fires. Plus offline AI for snake bites, CPR, hypothermia. We hope you never need it.
On the analytics side, Signal Radar competes within Health & Fitness, Travel and Artificial Intelligence — topics that collectively have 595.6k followers on Product Hunt. The dashboard above tracks how Signal Radar performed against the three products that launched closest to it on the same day.
Who hunted Signal Radar?
Signal Radar was hunted by Haifeng Cheng. A “hunter” on Product Hunt is the community member who submits a product to the platform — uploading the images, the link, and tagging the makers behind it. Hunters typically write the first comment explaining why a product is worth attention, and their followers are notified the moment they post. Around 79% of featured launches on Product Hunt are self-hunted by their makers, but a well-known hunter still acts as a signal of quality to the rest of the community. See the full all-time top hunters leaderboard to discover who is shaping the Product Hunt ecosystem.
For a complete overview of Signal Radar including community comment highlights and product details, visit the product overview.
Haifeng Cheng