Geekworm Raspberry Pi 4 X735 V3.0 Expansion Board with PWM Cooling Fan & Safe Shutdown & DC 6V-30V Width Voltage Input for Raspberry Pi 4B/ 3B+/ 3B / 2B: Amazon.de: Computer &
How to Make a Safe Shutdown Button for Raspberry Pi - Tutorial Australia
X735 V3.0 Power Management Board with Fan Safe Shutdown for Raspberry Pi 4B/3B/2 | eBay
GitHub - wware/rpi-shutdown: Circuit and scripts to provide graceful battery-backed shutdown for a Raspberry Pi 2.
Car Pi Power Auto Shutdown - Raspberry Pi Stack Exchange
PiZ SuperCap safe shutdown for Raspberry Pi Zero | Sub-Etha Software
Safe Shutdown and Auto Bootup for Raspberry Pi - Hackster.io