We do hear when we are asleep. That is why for example if the alarm goes you will wake up because you hear the ring. There are very many noises at night and if we woke up to every noise we would never get enough sleep. That is why our brains developed a mechanism to filter out noises. For example you can sleep even if the frogs are croaking very loudly. Our brains developed to ensure we only woke up to danger signals, like screams or shouts. The alarm or phone ringing or a baby crying wake us up because our brains have learnt that that is a signal that needs immediate response.
As for cats, have very sharp ears and can hear high pitched sound that we humans are not good at hearing. Also they have heightened sense of awareness at night than humans because they are night hunters (nocturnal) like dogs. They also have better vision at night. My cats sleeps all day because and is very inactive. As soon as it gets dark he runs out of the house and goes to play and hunt lizards outside 🙂