A sensor 100 for measuring temperature of an organism, comprises a first layer 104 in thermal connection with the organism, a second layer 122 comprising an insulating material and placed on top of the first layer； a first temperature sensor 110 in thermal connection with the first layer via the second layer, and a second temperature sensor 120 thermally insulated from the organism. The first and second sensors are located above the second layer. A third layer above the second layer may be provided, and comprise a metallic material. The sensor may have an electrical energy harvesting means and at least one energy storage unit. The sensor may further comprise a radiating element wherein the first layer is a reflector for said element, and an insulating material creates a distance between the antenna radiating element and the reflector. A method for estimating core temperature using the sensor comprises measuring the temperature from the first and second sensors and calculating the core temperature according to heat flux calculations using the measurements. Registering a mechanical input from the organism comprises recording a time for a detected mechanical input. The sensor may be used for measuring surface temperature of the organism.
