Physicists in the US have developed a new type of self-calibrating thermometer that exploits the shot noise in a tunnel junction to measure very low temperatures. Robert Schoelkopf of Yale University and colleagues at Yale and the JILA laboratory in Colorado say that their device is faster, more compact and simpler to use than conventional cryogenic thermometers (L Spietz et al. 2003 Science 300 1929).