You do not need sophisticated equipment to evaluate your child's hearing. You can use simple methods gauge your baby's hearing. For example, with an infant under six months old, check to see if the baby wakes up or cries when there is a loud noise, if the baby copies sound he hears, and if the baby turns his head in the direction of sound. See if the baby can recognize the sound of your own voice. You can also use methods like clapping behind the head, or banging pots and pans (my parents reportedly did that, though I was probably a toddler then).
It is a little trickier with a baby between six months and a year old. Both deaf and hearing babies babble in the earliest stages. So even if you hear your baby babbling it does not mean that your baby does not have a hearing loss. Based on my own experience, another good gauge is whether your baby increases his babbling over time. In fact, I have been told that I actually started to talk before they found out I was deaf. Legend has it that my first word was "up," then I stopped talking. Another gauge is how well your baby seems to understand when you say simple things or say your baby's name.
The older your baby is, the easier it is to judge if there is a hearing loss. Be aware of expected milestones in a baby's hearing development and if your baby is not meeting those milestones, it could be an indication of hearing loss. If a toddler is not responding to sound or speaking, that is a clear red flag to visit an audiologist for a hearing test.
Also, keep in mind that you should always go with your parental instincts. If you feel that your infant has a hearing problem but your pediatrician is brushing off your concerns, get it checked by an audiologist anyway.
Sources:
Is My Baby's Hearing Normal? http://www.entassociates.com/baby.htm
Raising and Educating a Deaf Child, p.112, Oxford University Press, 2007.
Your Baby's Hearing,
http://www.audiology.org/resources/brochures/Documents/YourBabysHearing.pdf
