How can I pair my Apple Magic keyboard to my mac without USB Cable?
I don't know if this was because of lower battery or just that it needed to be plugged in, but simply by connecting a charger (from the wall) to my keyboard and then going to MacBook's Bluetooth I was able to connect/pair it. 
This makes me wonder how you can avoid accidentally pairing another person's keyboard or potentially highjacking a few of keyboard strokes...



Credits: https://www.reddit.com/r/applehelp/comments/6z3u9k/is_there_a_way_to_pair_a_magic_mouse_without/dmsa4jk