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 .