Wageslave,
Afraid so old chap. Missile Warning Systems use the energy emitted from the Mx to "declare" the threat. Google
AN/AAR-47 (which is supposedly the Turkish AH-1 system),
AN/AAR-54 and AN/AAR-57 et al. As with most technology (e.g. NVGs..) they are only "discovered" when fitted to FJ; RW and AT (who spend far more time in the MANPADS envelope, in the case of the former 100%...) have had passive MWS technology for decades. You can also use radar, such as the
AN/ALQ-156, which detects incoming objects.