Now arises Mrs. Lydia McPherson of Los Angeles, California… Her friends claim that if Lady Godiva had possessed hair like Mrs. McPherson, she would have been more than adequately attired in her famous ride through the streets of Coventry. Mrs. McPherson surpasses Mother Eve, by wearing, as her picture shows, only nature’s covering, whereas the world’s first lady had to borrow from the fig tree. The tresses of Mrs. McPherson measure seven feet two inches from root to tip, and are of a find, bright red color.
San Francisco Examiner - Jun 26, 1927

Basically, the Songbird Saver consists of a small dummy bird which, when nudged by a cat for any reason, explodes.
Slattery's own news release describes its effectiveness perhaps more vividly:
"Slipping out of the house, the trainee-cat will make its stealthily stalking approach... Seeing it (the Songbird Saver), apparently frozen with terror, the trainee-cat will pounce upon it, and with the resulting explosion, that cat will go about 9 feet in the air and take off for the high timber before its feet touch the ground."
It is with this simple device that Slattery hopes to save civilization "as we know it."
"Songbirds are vital to our ecology of life," he explained. "Our society could not exist without them. Frankly, in six years we'd be up to our neck in insects."
Slattery emphasized his device is harmless to cats and uses merely the same sort of exploding caps used in cap pistols. It is based on common theories of preconditioning and some stuff he read by Mark Twain on a cat's ability to learn.
"It's based, actually, on a combination of Pavlov and Mark Twain. If both those guys are wrong, I'm wrong."
The dapper 54-year-old promoter denied he was "anti-cat" and said that in fact his invention would allow cats and birds to live together in harmony.