The Tale of KIISU: Slim Friend of Flipper Zero
It all started with a forgotten key. One quiet day, standing in front of a locked courtyard gate, the idea returned—something that had been on the mind for a while. What if there were a Flipper Zero-like device, but small enough to carry everywhere? Something so compact and light that you’d never leave it behind. That day, the seed of Kiisu was finally planted.
Named after the Estonian word for “kitten,” Kiisu was always meant to be small, cute, and deceptively capable. The goal wasn’t to replace Flipper Zero, but to offer a minimalist alternative—something that fit in your wallet, like a trusty sidekick always ready to pounce.
Inspired by the Dolphin
Flipper Zero was a natural inspiration. Its multifunctionality, its Tamagotchi-style appeal, and the robust community around it made it a dream tool for hackers and makers. But as handy as it was, Flipper wasn’t exactly pocket-friendly. We needed something slimmer.
So the design journey began. The first Kiisu prototype—what we now call V1—was a rough sketch come to life. It aimed to replicate Flipper’s core capabilities: Sub-GHz, NFC, RFID, IR, iButton, and GPIO. But everything had to fit onto a tiny board. Sacrifices were inevitable. The Tamagotchi-style pet behavior had to go, and to conserve battery, the device would shut down after a minute of inactivity.
To maintain compatibility with Flipper Zero’s firmware, we used a clever trick: inserting a second STM32 microcontroller between the main chip and the OLED screen. This secondary chip managed the display and even emulated components like the PMIC and fuel gauge. It was a hack—but a beautiful one.
V1 wasn’t without its flaws. SPI lines were crossed. Buttons were miswired. But that’s what prototypes are for. With the help of Oleg, our in-house wizard who can reroute hair-thin PCB traces with his bare hands, we turned those bugs into lessons. And soon, V2 and then V3 followed.
By Kiisu V3, we’d refined the board into something practical and powerful. It had a four-layer PCB with efficient power routing, compact battery options, and a sleek design with all components on one side. We even added environmental sensors, accelerometers, and a simple light sensor to detect flicker from screens and LED lamps.
Then came our most exciting evolution yet: Kiisu V4A.
With V4A, we reached a new level of polish. It retained the iconic credit-card size and sub-4mm thickness but added serious upgrades. A dual-MCU setup—featuring the STM32WB55 and STM32G431—gave us flexibility and power. BLE support finally made it in. The sensor suite grew smarter, now with compass, accelerometer, humidity, ambient light, and optional modules for air quality and distance sensing.
Powering Kiisu became more flexible, too. A USB-C connector now allowed for primary power or charging, alongside the classic CR2032/LIR2032 coin cell. Despite all this, Kiisu V4A stayed true to its roots: sleek, minimal, and quietly capable.
And the story doesn't stop here.
Kiisu V4B is already on the way! It features minor refinements and—most importantly—a fully polished firmware experience out of the box. We’re taking all the feedback, ideas, and edge cases and wrapping them into something ready for daily use.
Even more exciting, we’re beginning to flirt with the idea of a bigger vision: Kiisu One. Imagine a complete, integrated development platform—something that combines the agility of Kiisu with the maturity of a production tool. It would be plug-and-play, out of the box, and offer a robust platform for serious tinkerers and developers alike.
Kiisu began with a forgotten key. Today, it’s a growing family of tools, born out of necessity and driven by curiosity. We build it for people like us: makers, hackers, wanderers. And we’re just getting started.
Let us know what you’d love to see next.