Why is your baby such a light sleeper? You'd be surprised to know how many times you wake up in the night as well. However, babies lack the same faculties as you when it comes to putting yourself back to sleep. Self-soothing is a trait babies must learn over time. Although certain techniques will aid your baby in his quest to sleep all night, it is important to know the facts about baby sleep patterns.
The term "sleeping like a baby" doesn't really make sense in actuality- baby's actually have very different sleep patterns than adults. You may already know that REM sleep is a light sleeping period and the one in which we dream. However, did you know that a baby spends twice as much time as you do in REM? More sleep cycles = more chances of stirring awake. It is estimated that premature babies spend 80% of their sleep in REM.
Sleep cycles go like this: drift off into light sleep, then to REM, then deep sleep, then REM, light sleep, and back awake. Imagine it like a tide ebbing and flowing all night long. Typically, an adult's full sleep cycle is around 45 minutes long. Remember, babies are moving through their cycles a lot faster. That would explain those times that you think you are lying your sleeping baby down in his crib, only to see him burst awake screaming again- they don't sleep deeply as long or as often as we do.
If your baby is breathing slowly, steadily, and if his limbs are limp, then he is in a deep sleep period. (That would be your best shot at lying him down gently and sneaking out of the room.) However, you probably notice a lot of movement under your baby's eyelids (Rapid Eye Movement) and erratic breathing. This is normal for a baby. The older they get, the longer they will remain in deep, quiet sleep like an adult.
Sleep is crucial for everyone, especially baby and his developing mind/body. Make sure your baby is getting adequate rest. A newborn can typically sleep around 18 hours in a 24-hour period. An older baby, around 6 months, will typically sleep 3-5 hours in the day (combined time of several naps) and 10 hours at night. Consult your pediatrician if you are not sure about your baby's sleep schedule.