Designed by ZecTrix Lab in China, the Note 4 is an ESP32-S3-based AI smart note with a 4.2-inch e-paper display and built-in voice input. The reTerminal Sticky costs $49.99 and comes with a 3.97-inch touchscreen, while the ZecTrix Note 4 has physical buttons and a slightly larger 4.2-inch e-paper display. We have also written about other ESP32-based e-paper devices, including the open-source TRMNL 7.5-inch wireless E-Ink display, whose firmware is ported to the ZecTrix Note 4. We’ve also covered the ESP32-powered Inkplate series, including the Inkplate 6, Seeed Studio’s reTerminal E1001/E1002 e-paper displays, and the Merlot 4.2-inch e-paper display. Grok tells us it’s because the Note 4 comes with “lifetime AI voice task/reminder service”, but the color variant doesn’t.