login alarm / alarm
netctl. It is the Arch Linux built in network management system. If it isn't already installed (it should be though), run pacman -Syu netctl then look in /etc/netctl. There are example configuration files in /etc/netctl/examples. To use an example, just copy it to /etc/netctl and edit it to fit your set up. So for your case, run cp /etc/netctl/example/wireless-wpa /etc/netctl/somedescriptivename then edit /etc/netctl/somedescriptivename to fit your set up.
To enable auto configuration of your wireless networks with systemd, make sure the wpa_actiond package is installed and enable the service: systemctl enable netctl-auto@wlan0.service
https://wiki.archlinux.org/index.php/Netctl
wifi-menu -o
it generates the configuration file in /etc/netctl/ for the network to use for #Automatic operation at the same time
cp /etc/netctl/examples/wireless-wpa /etc/netctl/
Edit the profile as needed (modifying Interface, ESSID and Key) and it is done.
At this step you may want to re-confirm the new profile you created is chmod 600 and confirm it works by starting it:
netctl start wireless-wpa
before configuring any #Automatic operation.