BBpatrol 黑箱糾察隊

Context

BBpatrol is a driving safety app used in Taiwan. Drivers report mobile speed cameras and road conditions in real time; other drivers get voice alerts as they approach. It sits in Google Play's Maps & Navigation category and has crossed 5,000 downloads with a 4.3 star rating.

The problem

A driver watching the road cannot also watch a speedometer, and mobile speed traps move — a static database is out of date the day it ships. The only source that keeps up is other drivers.

That makes this a crowd-sourcing problem with a hard constraint: every interaction happens at speed, one-handed, with eyes that belong on the road. Anything requiring two taps and a look down is not just bad UX, it is dangerous.

What I built

• Built the app in React Native for Taiwan's driving market
• Implemented real-time GPS tracking with per-second position updates against reported speed trap locations
• Built the floating window overlay, so alerts stay visible over a navigation app rather than requiring BBpatrol to be foregrounded
• Implemented the voice alert system with multiple selectable voice packs
• Built the crowd-sourced reporting flow — one-handed submission of speed traps and road conditions while driving
• Integrated Line Login, the dominant auth method in Taiwan

Engineering challenges

Battery versus accuracy. Per-second GPS updates plus a persistent overlay is close to a worst case for battery. Tuning location accuracy, update frequency and background behaviour to stay useful on a long drive without draining the phone was the central constraint.

A UI you use without looking. Reporting has to be a single large target, confirmable by feel, with audio confirmation instead of visual. The voice packs are not a novelty feature — audio is the primary output channel, because the screen is not one.

Android overlay permissions. System overlay windows sit behind a special permission and behave differently across manufacturers' Android skins. Making the floating window reliable across real Taiwanese Android devices was ongoing compatibility work.

Localisation. The entire product is in Traditional Chinese for a Taiwanese market — a market I was building for without being in it.

Outcome

BBpatrol has passed 5,000 downloads on Google Play with a 4.3 star rating across 49 reviews, and is still receiving updates as of mid-2026.