Decades of research have shown that mice release a unique urinary odor. Further research suggests that a similar link may exist between the genes that control a human's immune system and his body odor. Who knew that a long-regarded nuisance could present opportunities for the security industry? The Pentagon's Defense Advanced Research Projects Agency (DARPA) is calling for $3.2 million in research funding to find out just how distinct those human odors are. The initial discovery phase of research is expected to last two and a half years, and it will determine whether "robust" fragrance signatures exist. It will also look at how they vary between individuals and are affected by stress, diet, health and age. If research supports the feasibility of odor detection, then DARPA will consider developing a sensor.The upside is that biometric identification technology based on odor could be much harder to trick than other biometrics because it would be based on people's genetic makeup as opposed to their fingerprints or retinal scans. The downside is that if biometric odor detectors ever make it to the market, the security checkpoints at airports could get a whole lot more embarrassing.