A differential pyroelectric infrared detector circuit comprising: - a pyroelectric crystal with two electrodes; - two separate impedance conversion circuits, wherein one impedance conversion circuit is connected to one of the electrodes and the other impedance conversion circuit to another of the electrodes of the pyroelectric crystal, wherein each of the impedance conversion circuits is formed from an amplifier and provides a first and second low impedance output (Output 1, Output 2); and - a differential amplifier for receipt of each of said low impedance outputs (Output 1, Output 2), so that the two low impedance outputs (Output 1, Output 2) are connected differentially; wherein either (i) the amplifiers forming the impedance conversion circuits comprise a FET (Q1, Q2), each electrode of the pyroelectric crystal is directly connected to the gate of the respective FET and the differential pyroelectric infrared detector circuit further comprises a primary bridge and a secondary bridge, wherein the primary bridge is coupled to each of the pyroelectric crystal electrodes and the secondary bridge is coupled to each of the amplifier outputs, wherein the primary bridge is formed by a first resistor and a second resistor, the primary bridge is furthermore coupled to the secondary bridge which is formed by a first resistor and a second resistor, and the primary bridge and the secondary bridge are connected to the ground potential, or (ii) wherein each of the amplifiers forming the impedance conversion circuits is an operational amplifier that has a resistor bridge (Zf1, Zf2) each of which is connecting the output with the inverting ("-") input of the corresponding operational amplifier, the electrodes of the pyroelectric crystal are directly connected to the inverting ("-") inputs of the operational amplifiers and wherein the non-inverting ("+") inputs of the operational amplifiers are connected to each other and to the ground potential. - a pyroelectric crystal with two electrodes; - two separate impedance conversion circuits, wherein one impedance conversion circuit is connected to one of the electrodes and the other impedance conversion circuit to another of the electrodes of the pyroelectric crystal, wherein each of the impedance conversion circuits is formed from an amplifier and provides a first and second low impedance output (Output 1, Output 2); and - a differential amplifier for receipt of each of said low impedance outputs (Output 1, Output 2), so that the two low impedance outputs (Output 1, Output 2) are connected differentially; (i) the amplifiers forming the impedance conversion circuits comprise a FET (Q1, Q2), each electrode of the pyroelectric crystal is directly connected to the gate of the respective FET and the differential pyroelectric infrared detector circuit further comprises a primary bridge and a secondary bridge, wherein the primary bridge is coupled to each of the pyroelectric crystal electrodes and the secondary bridge is coupled to each of the amplifier outputs, wherein the primary bridge is formed by a first resistor and a second resistor, the primary bridge is furthermore coupled to the secondary bridge which is formed by a first resistor and a second resistor, and the primary bridge and the secondary bridge are connected to the ground potential, or (ii) wherein each of the amplifiers forming the impedance conversion circuits is an operational amplifier that has a resistor bridge (Zf1, Zf2) each of which is connecting the output with the inverting ("-") input of the corresponding operational amplifier, the electrodes of the pyroelectric crystal are directly connected to the inverting ("-") inputs of the operational amplifiers and wherein the non-inverting ("+") inputs of the operational amplifiers are connected to each other and to the ground potential.