Best way to use router as a device tracker

Because of the battery drain of my iPhone I want to use my router as a device tracker (instead of location services on the phone). So I configured the OpenWRT Luci component in my HA configuration. It works like a charm when I switch off WiFi on my iPhone before leaving my home. HA then says iPhone: Away
When I simply leave my home without turning off wifi then the status stays: Home
This is because in the ARP table in the router the iPhone is still present.

Can someone advice me about the best way to use the router as a device tracker? Ubus, Ping, SNMP?

Since HA 0.59 it seems to be working with Luci!