The $54.99 kit, or $99.99 complete watch, adds Bluetooth Low Energy, an accelerometer, temperature logging and optional NFC to the classic digital watch.
Shand says the replacement board uses dual-core Cortex-M4 and M0+ processors, supports step tracking, gesture controls, interval timers, sunrise and sunset data, and simple games.
Aimed at users wanting less than a full smartwatch, it promises up to 10 months of regular battery life or three years in power-saving mode, with installation taking 10 to 15 minutes.
By ditching apps for extreme battery life, is this the wearable future that Big Tech completely missed?
Can upcycling classic watches with simple tech actually disrupt the industry's massive e-waste problem?