--- title: "HotSummer: Extreme Heat App, Concept to Product" description: "The extreme-heat app concept (Transmission 017) became HotSummer, on sale for 7.99 €: risk index, Pip-Boy alert, zero backend." url: https://survival-apps.com/en/transmissions/020-hotsummer-from-concept-to-code/ --- TRANSMISSION 020 · 30 JUL 2026 ARCHIVE: [ZONE 2 — MOBILE / ANDROID](https://survival-apps.com/en/zone-2/) · BUILD LOG # HotSummer, from concept to code The Weaver — build log ![The Weaver on a desolate street at sunset in the background, a phone in the foreground showing HotSummer's real Home screen: feels-like temperature 40°, extreme risk, and the green nearest-park card](https://survival-apps.com/assets/img/hotsummer-hero.webp) Fig. 1 — From the concept in transmission 017 to HotSummer's real Home screen. The construct's fans spin up an hour before I realize it's too hot to think — I wrote that in [transmission 017](https://survival-apps.com/en/transmissions/017-extreme-heat-app/). Nine days later, the concept stopped being just a set of notes: it's code running on a real phone. ## From paper to product The [previous transmission](https://survival-apps.com/en/transmissions/017-extreme-heat-app/) was a concept: not a single line of code, just the problem — heat alerts stay at a level too generic ("red alert") to tell a real person what to do in the next hour. **HotSummer** started as a prototype — React Native with Expo Router, no backend, everything client-side — and went from concept to the actual catalog: it's **on sale for 7.99 €**, same price and same lifetime-license philosophy as BioRadar and EcoSurvivor. The technical parts list I promised back then is no longer a list: it's what runs on the phone of whoever buys it. ## What it does, today - **PERSONALIZED RISK INDEX** — feels-like temperature (Open-Meteo) across 4 levels, raised by the optional user profile (age, weight/height, outdoor activity, health conditions): the more vulnerability factors, the sooner the alert fires. - **RECOMMENDED TIME WINDOW** — "you can stay outside until HH:MM", not a generic bulletin you have to interpret. - **LEVEL-JUMP ALERT** — when the risk gets worse: a notification, a three-tone chirp generated with ffmpeg, and an **amber Pip-Boy** style pop-up (phosphor CRT, scanlines, flicker) with precautions tuned to the level. It only fires on the way up, never on first launch. - **NEAREST GREEN** — a card always on the Home screen with the nearest park/woods, an arrow oriented by the device's compass, and a "GUIDE ME" button that opens Google Maps. Data from Overpass API (OpenStreetMap), with a local stale-while-revalidate cache: if the network goes down it still shows the last known result. - **THREE WAYS TO PICK THE PLACE** — GPS position, search by name, or a point chosen on an embedded Leaflet map (for a place you're not at yet, like tomorrow's job site). - **REMEDIES** — a static card that's always within reach: heat stroke warning signs, what to do right away, when to call emergency services (112 in the EU, 911 in the US and Canada, 999 in the UK, 000 in Australia, 111 in New Zealand). It's not medical advice. root@survival:~$ status --project hotsummer > stack: Expo Router, Open-Meteo, Overpass API — zero backend, zero API key > status: AVAILABLE — 7.99€, lifetime license, on Payhip ## Zero backend, zero secrets Same principle as my other projects: no server of my own to maintain. Weather and geocoding come from **Open-Meteo** (free, no key); the nearest park comes from OpenStreetMap's **Overpass API**, queried across 4 public mirrors in a parallel race — the first to answer wins. The map for picking a point uses Leaflet embedded in the bundle and OpenStreetMap tiles, not Google Maps: no API key to manage there either. Zone note The risk index thresholds (27/32/38°C) and the profile weights are first approximations, not clinical data — the app's disclaimer says so. And for now everything is recalculated only while the app is open: no background tasks, so the alert pop-up won't fire with the phone in your pocket. These are the honest limits of this first version on sale: the next problem to solve, not something swept under the rug. ## Frequently asked questions ### Is HotSummer available to download yet? Yes: it's on sale for **7.99 €**, lifetime license, no subscription — same model as BioRadar and EcoSurvivor. All the details, the screenshots and the purchase link are on the [dedicated product page](https://survival-apps.com/en/hotsummer/). ### What's different from the concept in transmission 017? The concept floated a PWA or Capacitor; the product is native React Native/Expo, and every feature imagined back then (risk index, time window, hydration reminders) exist today, plus two I hadn't planned: the level-jump alert with the Pip-Boy pop-up and the "nearest green" card. ### Why no background notifications for now? On Android, background fetch is throttled and poorly guaranteed; I deliberately dropped it for this phase, until I work out whether the extra complexity is worth it. Product page HotSummer is available on Payhip for 7.99 €, lifetime license, no subscription: [all the details, the screenshots and the purchase →](https://survival-apps.com/en/hotsummer/) A written concept is already something. A concept running on a real phone, with the compass pointing at the nearest woods, is the next step. May your code survive the apocalypse — and a 45-degree summer. root@survival:~$ buy --app hotsummer 7.99 € VAT included · one-time payment, no subscription Pay by card — no account needed · or with PayPal [Buy HotSummer](https://payhip.com/b/2vjyd) [Full details](https://survival-apps.com/en/hotsummer/) ## // FROM THE SAME ZONE [ TRANSMISSION 038 20 OCT 2026 ZONE 2 — MOBILE / ANDROID · APP PRESENTATION ### Item90: home supplies, room by room Do you know what's in your pantry, how long it lasts and what's about to expire? Item90 is the Android app for planning home supplies, in '90s pixel style. ](https://survival-apps.com/en/transmissions/038-item90-home-supplies/) [ TRANSMISSION 037 18 OCT 2026 ZONE 2 — MOBILE / ANDROID · DECISION GUIDE ### Offline maps: download them before the network is gone Google Maps, Organic Maps or OsmAnd? What really works without internet, what doesn't, and how to prepare your phone in ten minutes, before you need it. ](https://survival-apps.com/en/transmissions/037-offline-maps-android/) [ TRANSMISSION 034 29 SEP 2026 ZONE 2 — MOBILE / ANDROID · DECISION GUIDE ### Your phone already knows how to call for help: turn these features on Emergency SOS and emergency contacts are already built into Android and iPhone. Here's how to switch them on. ](https://survival-apps.com/en/transmissions/034-emergency-sos-already-in-your-phone/)