How is carbon dioxide level in breath checked?

Most of you may be aware that oxygen level in blood can be easily checked by keeping a small device known as pulse oximeter on your finger. But carbon dioxide level cannot be checked with that device. Blood carbon dioxide level can be checked by taking a blood sample from the artery and analyzing it in the blood gas analyzer.
Artery is a blood vessel carrying oxygenated blood to a part of the body. Carbon dioxide level in the air you breath out can be checked by collecting a small sample and analyzing it in a device. Instantaneous values can be displayed on a monitor as well.