In the past, it was a common belief that snakes couldn't hear much if anything since they have no external ears and don't seem to respond to noises. However, scientific research refutes this common misconception.
Snake Ear Anatomy
Many people don't realize that snakes have ears but they are in fact there. Directly behind their eyes, snakes have two ears just like other reptiles. They do not have external ears (commonly referred to as ear flaps, pinnae, or auricles), but they do have small holes on the sides of their head that are ear openings. Inside each tiny ear-hole is a functional inner ear but no eardrum (tympanic membrane) or middle ear. The inner ear is filled with air in snakes while most other animals have fluid-filled inner ears.
How Snakes Hear
As previously mentioned, snakes do not have external ears (pinnae) or eardrums like we do but they do have fully formed inner ear structures. In addition to their inner ear structures, they have a bone called the quadrate bone in their jaws. This bone moves slightly in response to vibrations while they slither on the ground.
For many years it was undetermined whether or not snakes could hear noises that were not ground vibrations. Research has since shown that this quadrate bone does, in fact, respond to airborne vibrations as well as ground vibrations (thought to be due to spinal nerves that have conducted the vibrations from the skin recognizing them and causing the quadrate bone to vibrate, referred to as somatic hearing). As with other animal ears, this movement is transferred (via bones) to the inner ear and then signals are sent to the brain and interpreted as sound.
What Snakes Can Hear
Pitch (high or low sounds) is measured in Hertz (Hz) and how quiet or loud sounds are is measured in decibels (dB). Hertz is primarily what researchers have measured to determine whether or not a snake has the ability to hear. Some researchers determined that snakes are able to detect low frequency airborne and ground vibrations through their inner ears (in the 50 to 1,000 Hz range) but a lot is still not understood regarding exactly what a snake can hear. Some studies show that their peak sensitivity is in the 200 to 300 Hz range while others show it in the 80 to 160 Hz range.
A person with great hearing abilities can hear anything between 20 to 20,000 Hz. 20 to 25 Hz is described as the lowest sound that a pipe organ can make or the sound of a low cat purr while about 4,100 Hz is the highest note a piano can make. Using this knowledge we now know that snakes can only hear what we would consider lower sounds.
Since different breeds of snakes have been used for various studies, it is still difficult to make a blanket statement regarding all snakes and hearing. We assume all snakes have similar hearing abilities since they have the same ear anatomy, but it is possible that snakes from different environments are able to hear different ranges of sounds.
Since we know that the peak sensitivity of a snake's hearing is in the 200 to 300 Hz range and the average human voice is at about 250 Hz we can determine that a pet snake can, in fact, hear you talking to them. This supports what many snake owners claim—that pet snakes can recognize their names being called.
Knight, K. Snakes Hear Through Skull Vibration. Journal Of Experimental Biology, vol 215, no. 2, 2011, p. ii-ii. The Company Of Biologists, doi:10.1242/jeb.069104
Christensen, C. B. et al. Hearing With An Atympanic Ear: Good Vibration And Poor Sound-Pressure Detection In The Royal Python, Python Regius. Journal Of Experimental Biology, vol 215, no. 2, 2011, pp. 331-342. The Company Of Biologists, doi:10.1242/jeb.062539