An ingenious new cat collar could bring cheer to the feathered population and prevent the deaths of millions of wild birds killed by domestic cats every year.

The collar - memorably called The Liberator - emits an audio and visual alarm when a cat launches itself from the ground to attack a bird. The alarm is activated by the force of propulsion. The early warning gives the bird enough time to take flight and escape. The frequency of the audio alarm means that, although it sounds threatening to birds, it does not alert cats or humans.

The alarm's maker, Khazu, says the collar, which weighs about the same as a box of matches, warns the intended prey but does not restrict the cat's natural movements or actions. Cats continue to hunt as normal, but have no chance of catching bird life.