A naturally collimated surface acoustic wave (SAW) propagating around the equator of a sphere hundreds of times was discovered by Yamanaka et. al. Since this unique propagation phenomenon enables to cumulate small changes of the SAW in amplitude and/or delay time caused by its environment, it works as extremely sensitive, fast response chemical sensor. It is called as “ball SAW sensor”. Sensing gas component can be determined by a sensing film coated on the surface of the sphere. Applications of the ball SAW sensor such as trace moisture sensor, hydrogen sensor, portable gas chromatograph and airborne virus sensor are introduced.