The device was first mentioned in "The Luminous Fish Effect" by Mary Cooper while she was telling a story about Sheldon's childhood. Sheldon was devastated when the government inhibited his nuclear reactor work. Then he built a "sonic death ray" which did not slow down the neighbor kids but pissed of their dog.
In "The Ornithophobia Diffusion", the Ultra Sonic Blaster is a high-frequency tone generator Sheldon uses on the Black-throated Magpie-Jay (later known as Lovey-Dovey) on his window sill in an attempt to scare it away.
The device was set up by Howard, who dubbed it a "Bird Death Ray", but it fails to execute its intended purpose, instead cracking the apartment window and not affecting the blue jay at all.