Sometimes Kitty perks up at seemingly nothing. He may run to the door to greet someone before you've even realized anyone was there. Kitty isn't clairvoyant, but he does have excellent hearing. Not only can he hear very quiet and high-pitched sounds, but he can pinpoint them with deadly accuracy.
The frequency range that Kitty hears in favors high-pitched noises. His threshold for low noises is about the same as ours, 30 hertz (Hz), which refers to 30 cycles per second. The highest pitched noises we can hear are around 20,000 Hz or 20 kHz. Kitty can hear sounds up to 65 kHz, which is almost two octaves higher than you. This allows kitty to hear the tiniest squeak of a mouse or a mother cat to recognize the quiet mews of her kittens. This also means Kitty will respond more frequently to a woman's or child's voice, since they're typically higher pitched.
Satellite Dish Ears
Kitty's ears function a little like a satellite. They're large and allow him to hear sounds from about five times further away than you can. They also swivel. Unlike humans who have to turn their head to hear a sound, Kitty's ears rotate 180 degrees. You'll notice him twitching them frequently to determine where an interesting noise is coming from. This gives him the ability to stalk and locate his prey from long distance without being detected.
Not only can Kitty hear the most minute of noises, but he can pinpoint their location. From up to three feet away, he can determine a noise's location with accuracy within inches in only 6/100 of a second. Kitty's hunter brain is hardwired to detect the time delay in the arrival of a sound, allowing him to determine it's location. He can also pick up on variances in noises of only 1/10 of a tone. He'll use this information to determine exactly what type of prey, maybe a mouse or a lizard, is making the noise.
Occasionally, cats either are born deaf or lose their hearing over time. The causes could be an infection or trauma to his ear. Long-term exposure to loud noises can cause Kitty's hearing to weaken. As he ages, his ear drum thickens and he will not be able to hear as well as he did when he was young. If Kitty doesn't respond when you call him anymore, paws at his ears or startles easily these are all signs of hearing loss. If you think he may be going deaf, have him visit his vet to have his ears tested. Some causes, like infection or tumors, could be reversible.