I know where you lived last summer: a "hair-brained" method for tracking people

Researchers have discovered that isotopes in the water you drink are incorporated into your hair as it grows. It also turns out that those isotopes have a high correlation with U.S. geographic regions: this means that a single strand of hair can give researchers a lot of hints about where you've lived for the duration of that strand's life. The longer the strand, the more data it's recorded.

The locations are imprecise: your hair won't reveal which neighborhoods you've hung out in Cleveland, but the method has already been effective for detectives. They've used strands from a murdered "Jane Doe" to narrow down the region she lived in for the last two years of her life, and believe the technology will be helpful in tracking serial killers.

While you could try to trick the system by only drinking bottled water from Maine, but scientists say that it's hard to avoid the isotopes from your home town. They're in your soup, coffee, ice, and even pasta boiled in local water. So if you suspect that your husband's last extended "business trip" was to Texas, when he told you it was Minnesota, just pluck a strand from his pillow and bring it to the lab. We can't decide if that's more or less creepy than hiring a private investigator.

Technology Review