The safety beacon is a device in the form of a small thin wooden structure given to Annie by Eglamore on Chapter 20, Page 8 to use 'at the first sign of trouble' and which summons him within 5 seconds.
Annie needed to use it to escape Ysengrin when he became enraged about Coyote's Great Secret, thinking that Annie was laughing at him. It was used on Chapter 39, Page 27.
Its nature or how it works is currently unknown, though the valknut symbol that appears when it was used and teleportation effect suggests a relationship with Brinnie (who may or may not be Brynhildr, the Valkyrie).
Safety beacon being given
Annie about to break the safety beacon
Teleportation of Eglamore via safety beacon