Telomeres are DNA repeats at the ends of chromosomes. Their function is to maintain the integrity of chromosomes. Telomeres are shortened every time DNA is copied. Once telomeres are exhausted, chromosomes are prone to mutation, leading to arteriosclerosis or cancer. 
Using telomere for life length detection will bring inner tension and anxiety to the subjects, and the results may lead to relevant ethical and moral problems
 some people speculate that the length of telomere DNA can be used to calculate people's life span.