Detecting a bomb in a public space like a bus or a building is technologically doable, according to engineers and researchers working on such devices today. The solutions won't come cheap, and it will be at least a year before devices sensitive enough to prevent disasters like last week's bombings are deployed. But "when terrorists are willing to go to the extremes we have seen, the one thing we have to fight them is technology," said Bonner Denton, a professor at University of Arizona. Denton has invented a capacitive transimpedance amplifier that he claims increases the sensitivity of ion-mobility spectrometers by a thousandfold, thereby enabling 100 percent of passengers to be efficiently screened. Denton collaborated with researchers at Sandia National Laboratories (Albuquerque, N.M.) to develop the device. Sandia is using it in a "microhound" explosives detector that it says will replace bomb-sniffing dogs.