EZ Fuse Tester

EZ Fuse Tester is the smallest, most focused app we have ever shipped, and one of the most successful. It is a free utility that turns an iPhone screen into a continuity tester for small glass cartridge fuses, using the phone's built-in capacitive touch sensors to detect whether the fuse is intact or blown. The whole app is one screen. There is no signup, no account, no in-app purchase, no ads, and no data collection.

The full story of how the idea showed up on a Tuesday evening in October 2023 is in our journal post on what we learned shipping EZ Fuse Tester. This case study is the structured version for clients trying to understand whether we are the right team for a small focused utility project.

The problem

The original problem was personal. A string of Halloween lights stopped working. Somewhere in the plug was a tiny glass fuse that had blown. The replacement fuses that supposedly came with the lights had been gone for years. The nearest hardware store was closed. Testing each fuse with a multimeter meant disassembling the plug, which is slow.

The general version of that problem applies to anyone who works with small electronics. Automotive enthusiasts. People who restore old radios or stereos. Anyone with a soldering iron and a workshop. The fuses themselves are cheap. The hassle is testing them to figure out which one needs replacing.

The opportunity was to use a device almost everyone already owns, the iPhone, to solve the problem for free.

The approach

A standard glass cartridge fuse is two metal end caps connected by a thin filament inside a glass tube. When the fuse is good, the filament is intact and the end caps are electrically connected. When the fuse is blown, the filament has melted and the end caps are isolated.

An iPhone screen is a capacitive touch sensor that detects changes in the local electric field. A continuous piece of conductive material laid across the screen registers as a connected touch zone. A broken piece of conductive material registers as two separate touch points.

The app uses the multitouch detection APIs in UIKit to look at what is touching the screen when the user lays a fuse across the marked area, and reports PASS or FAIL based on whether the touches form a single connected region or two isolated regions.

The implementation is a few hundred lines of Swift. There is no networking code. There is no backend. The whole app fits in a few megabytes.

The launch

EZ Fuse Tester shipped to the App Store about three weeks after the original idea. App Review approved it on the first submission. We chose to release it free, with no ads and no data collection, because the app's value is in being available at the exact moment someone needs it. Friction at install or use would defeat the point.

The privacy policy is one sentence long. The marketing site is the App Store listing.

What App Store users have done with it

The reviews are some of the most fun we have to read. People have used the app to fix Halloween lights, Christmas lights, classic British car wiring, vintage Sony reel-to-reel tape deck fuses, soldering iron stands, lamp restorations, and countless other small electronics. The common theme across the reviews is relief. Someone was about to throw something out, the app saved them from doing so, and they wrote to say thank you.

The most surprising part of the launch was the second-order effect on WildTech as a company. Tradespeople and electronics hobbyists started sharing the app in forums and discord servers. Each of those mentions was implicit social proof for the larger studio that we never could have manufactured on purpose.

Why this matters for clients

If you are trying to figure out whether WildTech is the right team for a small, focused utility app, EZ Fuse Tester is the proof. We will not over-engineer it. We will not try to talk you into a subscription you do not need. We will ship something that does its one job well and gets out of the way.

If you have a small focused utility idea that should exist, let's talk about how to make it real.