Why don't you wake up when you hear a sound only once?

Question

Why don't you wake up when you hear a sound only once. e.g an alarm clock bleeping once?

Answer 1

I do..

Answer 2

Some do....

Answer 3

Some people do, it depends on how much of a heavy sleeper you are.

Answer 4

How do you know that you didn't waken if you heard it ?

Answer 5

you may be in a deep sleep.

Answer 6

I dont generally wake up to my alarm clock at all, so i cant really help.

Answer 7

When we are sleeping, our brains are biologically programmed to respond to unusual sounds which seem to be incongruent with normal audio emissions.  One short tone is usually translated as a random, superfluous noise which must be replicated more than once to be identified as something unusual enough to be consciously aware of.