A surface acoustic wave (SAW) creates its own high-Q ultra-small volume whispering gallery modes (WGMs), different from usual bulk acoustic WGMs, in an optical dielectric WGM resonator. We show that it is possible to realize an externally controllable, efficient triply-resonant opto-mechanical interaction between two optical WGMs and the SAW WGM and to use such an interaction in various sensor applications.The prediction of surface acoustic waves (SAWs) [1] and the study of whispering gallery modes (WGM) in acoustic resonators [2] are amongst numerous contributions of Lord Rayleigh, nee John William Strutt, to physics of waves. In the hundred or so years that followed the inception of these branches of acoustics, SAWs have been extensively studied and widely used in various electronic applications, particularly as sensors, oscillators, and filters. The notion of WGM resonators has been extended to photonics to serve as a tool in many applications in linear and nonlinear optics. With the advent of cavity opto-mechanics in recent years (see [3,4] for review) it is natural to ask if there is a way to devise a system where optical WGMs interact, or lead to, mechanical SAWs. At first glance it might be concluded that optical and SAW WGMs do not interact efficiently because SAWs do not change the volume of the resonator. In this work we describe a system of three WGMs in a dielectric resonator, whereby two optical modes combine to generate and control a mechanical SAW. The resulting acoustic wave is of extremely high quality factor (Q) and can be optically cooled to quantum level. Such a system, interesting from the scientific point of view, can have important applications in quantum technologies and will significantly enhance the sensitivity of SAW sensors. As an example of these applications, we describe a high sensitivity "absolute temperature" thermometer capable of operation outside the controlled environment of metrological laboratories.Opto-mechanics relies on interacting high-Q optical and mechanical modes [3,4] that can be used for manipulation of both classical and quantum states of the optical as well as mechanical modes. For instance, the dynamic back action of light onto a long lived mechanical mode of a resonator allows either a significant reduction of the mode temperature or an efficient transfer of the optical energy to the mechanical mode, depending on the experimental conditions. The temperature reduction results from conversion of thermal phonons populating the mechanical mode into optical domain, similar to the case of laser cooling in atomic systems. Hence cooling occurs when frequency of light increases as a result of interaction with the mechanical mode. Enforced decrease of frequency of the scattered light results in heating and oscillation of the mechanical mode.The basic practical task of cavity opto-mechanics is related to fabrication and integration of resonant micromechanical and optical elements, which interact efficiently. The efficiency of the interaction increases with an increase of ...