Intermediate frequency unsteady temperature measurements using small size suction pyrometer are reported. Off-radiation losses are proven to be not neglectable in contrast to what is assumed by others. To compensate for off-radiation energy loss the sensor is covered with high temperature resistant ceramic wool through which suction is applied. Overall response increased several times compared to a micron size bar thermocouple in the same environment. The pyrometer is used to measure oscillating temperature in a mechanically interrupted flame and in a pulse combustor. A theoretical analysis of heat transfer is presented for an idealized thermal system. The solution for a set of integro-differential equations has been used in parametric analysis of the new measurement technique. The results show the contributing effect of the ceramic wool in compensating for the radiative flux from the sensor. The heat balance for a harmonically oscillating temperature was obtained that allowed the monitoring of instantaneous gas temperature, frequency and phase shift.