Obtain client's MAC address using Node js

I'm working on a project that will allow my home automation identify who is at home by using their MAC addresses as an identifier.

I've tried to obtain the MAC address of a client on my own network using Nodejs and the NPM module 'arped'

var arped = require('arped');

console.log(arped.table());

It reads the ARP tables though it only outputs a handfull of IPs/MACs. Is there something that I'm missing about ARPs or what?

The output is showing my router, my chromecast, my windows laptop and my iPhone 4. It's not showing another windows laptop and an iPhone SE.

via Paul