Thinking of pulling off the perfect crime? Here’s one more thing you now need to take into account (thanks for nothing, science): your saliva. Yes, it’s no longer enough to keep track of every single hair, every last skin cell, and and absolutely everything you touch at the scene of your nefarious scheme. Researchers at UCLA have figured out how to determine age to within five years from nothing more than a saliva sample.

The method relies on a process called methylation, which is a chemical change to one of the four building blocks of a person’s DNA. Methylation changes as our bodies grow older, contributing to age related diseases. In extracting DNA from saliva samples from more than 100 test subjects, the team found that it could zero in on a person’s age within five years by looking at just two of the 3 billion blocks that make up the human genome–such is the strong correlation between methylation and age.

But the approach could go beyond simply being a forensic tool employed at crime scenes. DNA age (or “bio-age”) doesn’t always line up perfectly with chronological age. So methylation doesn’t always give a precise chronological accounting of years gone by (hence the five year margin of error–still very precise by existing standards). But it does tell you how old you are in DNA years, so to speak.

So physicians could use the unobtrusive saliva analysis to determine patients’ bio-ages, tailoring medical tests and interventions to a person’s bio-age rather than his or her chronological age. That means fewer unnecessary tests and a better, more effective application of medical science to prevent age-related illnesses.