The ARP Scan Tool is a very fast ARP packet scanner that shows every active IPv4 device on your subnet. Since ARP is non-routable, this type of scanner only works on the local LAN (local subnet or network segment).
The ARP Scan Tool shows all active devices even if they have firewalls. Devices cannot hide from ARP packets like they can hide from Ping. To find active IP addresses outside your subnet, use the Ping Scan Tool (a Ping Sweep tool AKA NetScanner).
$ sudo arp-scan -l -g