An infrared motion detector including at least one infra-red radiation sensor, at least one radiation reflecting surface, operative to direct radiation impinging thereon towards the at least one infra-red radiation sensor and at least one coating layer, coating the at least one radiation reflective surface, which is substantially reflective to far infra-red radiation and which strongly absorbs at least one of visible light and near infra-red radiation, wherein the at least one coating layer includes black nickel.