Recommended · for beginners
The Borkin Button Easy Raspberry Pi Power Button
Why people recommend it
Offered as a simple way to add a power on and off button to a Raspberry Pi using the audio socket and one soldered wire.
Watch for: Uses up the audio jack and needs light soldering
In their words
I have installed a jack button to turn on and off my raspberry pi 3 following the method described in the youtbue video The Borkin Button Easy Raspberry Pi Power Butto.
Blue on raspberrypi.stackexchange.com, Oct 2017. CC BY-SA.