Horn of Summons
This steel battle horn alerts even those allies you cannot see.
Wondrous Item 2,600 gp
Power Encounter (Standard Action)
When you sound the horn, all creatures within 1 mile hear its call. Allies within that range are awakened if they are sleeping, and instantly know your current location, hit point total, and any effects currently affecting you.
Published in Adventurer's Vault, page(s) 173.