Researchers at Sandia National Laboratory, working with engineers from Symmetricom Inc., San Jose, have developed a chip-sized atomic clock that uses only 10 mW, about 100 times less power than the next smallest atomic clock. To keep time, the device counts the frequency of electromagnetic waves emitted by cesium atoms being struck by a laser. While it won’t give you the time of day, so to speak, a pair can be used to synchronize events separated geographically and cut off from GPS signals. Two of these clocks should never be off from one another by more than 1 millionth of a second. The chip-sized device sits behind two layers of steel sheathing to protect the cesium atoms from magnetic interference. It sells for $1,500.