lu·men /ˈluː.mən/ · noun — the SI unit of light
I'm Lumen — founder and engineer from Lake Constance, Germany. I turn ideas into shipped products: an AI accountability coach, an ad-personalization SaaS and a Chinese-learning app. And I document the whole journey.
/ 01Ventures
Three products, three problems I couldn't leave unsolved. Built end-to-end: idea, validation, design, code, launch.
The AI coach that shows up for you.
Most productivity apps wait for you to open them. Tier doesn't. Your AI accountability coach checks in proactively every single day, breaks big goals down from year to today, and runs weekly reviews that ask the hard questions.
One landing page that matches every ad.
Ad clicks die on generic landing pages. Adfit personalizes headlines, copy and CTAs in real time based on the exact ad that brought the visitor — with AI suggestions, built-in A/B testing and one snippet that works on any stack.
one page · every adGoogle Ads · “rental income”
Turn your property into effortless income
Master Chinese characters. Smarter.
Learning Chinese fails when practice doesn't stick. Zimo combines spaced repetition, guided character discovery and smart reminders into a daily habit loop — pronunciation, vocabulary and context in one place.
字
zì · character
/ 02Story
From measuring radiation at Switzerland's largest research institute to building products of my own — the throughline was always the same: understand the system, then build something with it.
Age 16
Spent my teenage years at a student research center. With my Jugend forscht team, built a prototype process-engineering plant — and won Germany's national prize for the best interdisciplinary work.
Age 19
Fixed people's computers and built their websites. Learned early that shipping something real beats talking about it.
University
Furtwangen University. Risk and safety engineering by day — Ethereum mining rigs humming at night.
2.5 years
Paul Scherrer Institute — Switzerland's largest research institute and home of the Swiss Light Source. My job: measuring and managing the kind of light you have to respect.
haendler.dev
Left the safe path, went self-employed. Designed and shipped websites, web apps and mobile apps for clients — Next.js and React Native, end to end.
Today
Building Tier, Adfit and Zimo. Documenting the journey as @schlumen. Turns out the safest bet was betting on myself.
/ 03Content
Short-form videos about building products, biohacking and the founder life — published as @schlumen (mostly in German). Shot, cut and graded in my own editing pipeline.
/ 04Life
My body is the longest-running system I maintain. Sleep, training, nutrition and bloodwork are tracked like production metrics — measured, versioned, continuously improved. The results end up on camera.
21.1 km
Half marathon
Race day · 11 Oct 2026
100 kg
Bench press · 3×5
2026 strength goal
10–12 %
Body-fat target
By end of 2026
24/7
Tracked & measured
Whoop · bloodwork · protocols
/ 05Markets
Bitcoin and crypto investor since my Ethereum-mining days at university — through more than one full market cycle. And honestly? The charts out-earn everything else I do. On Telegram I share technical analysis, setups and honest market takes.
BTC / USD · higher timeframe
No signals-group hype, no moon promises — chart structure, levels and risk, explained the way an engineer thinks about systems. If you like slow, deliberate analysis in a fast market, you'll feel at home.
Join the Telegram channel/ 06Work with me
I take on a handful of engineering and product projects — full-stack builds with Next.js and React Native, MVPs shipped end-to-end, and honest technical advice from someone who ships his own products. If it's ambitious and needs to actually launch, I'm interested.
