Abstract: An ambient condition sensor is embodied in an oscillator which generates an output signal having a frequency which is proportional to the ambient condition of the environment in which it is located. The oscillator includes a ring resonator consisting of a metallic ring located in the output plane of a grounded source gallium arsenide MESFET type transistor oscillator formed on a temperature sensitive dielectric substrate. The circumference of the ring is directly related to the ring resonator's resonant frequency. More particularly, the circumference of the ring is a multiple of the wavelength of the oscillator's output signal. Such a device permits unmanned, remote and inexpensive temperature sensing in places generally unsuited for operator presence.