A passive infrared, PIR, sensor system comprising: - a first PIR sensor associated with a first sensing region, the first PIR sensor comprising a first sensing element configured to sense heat radiation from a first group of zones of the first sensing region and a second sensing element configured to sense heat radiation from a second group of zones of the first sensing region, wherein the first sensing element and the second sensing element of the first PIR sensor are distinct, and the first and second group of zones of the first sensing region are also distinct, - a second PIR sensor associated with a second sensing region, the second PIR sensor comprising a first sensing element configured to sense heat radiation from a first group of zones of the second sensing region and a second sensing element configured to sense heat radiation from a second group of zones of the second sensing region, wherein the first sensing element and the second sensing element of the second PIR sensor are distinct, and the first and second group of zones of the second sensing region are also distinct, wherein the first and second sensing regions partially overlap such that a zone of the first sensing region overlapping a zone of the second sensing region defines a detection cell (46a-46f) and a non-overlapped zone defines another detection cell (45a-45d), wherein each detection cell is represented by a predetermined amplitude and a predetermined sign of a first output signal based on input signals from the first and second sensing elements of the first PIR sensor and a predetermined amplitude and a predetermined sign of a second output signal based on input signals from the first and second sensing elements of the second PIR sensor, the PIR sensor system further comprising: - a processing unit configured to associate the amplitude and sign of the first output signal and the amplitude and sign of the second output signal with one of the detection cells for determining in which of the detection cells a heat source is positioned. - a first PIR sensor associated with a first sensing region, the first PIR sensor comprising a first sensing element configured to sense heat radiation from a first group of zones of the first sensing region and a second sensing element configured to sense heat radiation from a second group of zones of the first sensing region, wherein the first sensing element and the second sensing element of the first PIR sensor are distinct, and the first and second group of zones of the first sensing region are also distinct, - a second PIR sensor associated with a second sensing region, the second PIR sensor comprising a first sensing element configured to sense heat radiation from a first group of zones of the second sensing region and a second sensing element configured to sense heat radiation from a second group of zones of the second sensing region, wherein the first sensing element and the second sensing element of the second PIR sensor are distinct, and the first and second group of zones of the second sensing region are also distinct, wherein the first and second sensing regions partially overlap such that a zone of the first sensing region overlapping a zone of the second sensing region defines a detection cell (46a-46f) and a non-overlapped zone defines another detection cell (45a-45d), - a processing unit configured to associate the amplitude and sign of the first output signal and the amplitude and sign of the second output signal with one of the detection cells for determining in which of the detection cells a heat source is positioned.