"It's a ring for a friend. They're not wizards, so the charm needs to be self-sustaining. As it stands now, I can charge it for them every so often, but if I'm not around, I don't want it to suddenly quit. What is does is act a bit like Hot and Cold - you know, the game? One party has a ring, the other a coin, and they can 'ping' each other and try to narrow down a direction."

As Harry speaks, it's obvious he's put some thought into this already and what first looks like vague gestures with his hands quickly solidifies into sketches of charm pathways that hang in the air between them.