The configuration UI for this is a bit deceptive, since it only mentions activating the mode when a phone connects on the network, but it works both ways -- i.e. when the phone is gone the hub will switch back to regular operation if the earlier switch to home/disarmed happened due to the appearance of the phone. Note, however, that with iphones there is a delay of something like 20 minutes before the mode switch, because it's hard to decide when an iphone is gone ... i.e. the phones can sleep for a long time even when technically connected, so we have to wait long enough to be confident that the phone is gone.