Chemical tests for pregnancy, as you can read above, look for the presence of the beta subunit of hCG (human chorionic gonadotropin) in the urine or blood.
Most home pregnancy tests, which detect hCG in urine, are based on what is known as lateral-flow technology. This type of tests (lateral flow tests or lateral flow immunochromatographic assays) work by detecting the presence or absence of a target analyte in a sample.
Lateral-flow technology is based on the use of capillary beds, e.g. microstructured or sintered polymer, or pieces of porous paper, which are able to transport fluid rapidly.