The firmware runs on M5Stack’s PaperMono (about $65): an ESP32-S3 with a 3.97-inch, 480×800 e-paper touchscreen and a 1150 mAh battery. Wi-Fi switches on only to sync — hourly, right after an edit, or on a tap if the list is more than five minutes stale — so it otherwise sits on the fridge fully offline, grouped by aisle in the order you walk the shop. A self-hosted server keeps every phone in sync and can optionally sort new items into aisles with Claude; about 2,400 lines of C++, GPLv3.