AR15 Back Up Iron Sights or BUIS are used by AR shooters to provide co-witness set ups or to practice shooting without optics. Check our selection of flip-up rear and front AR15 sights and more ! Electronics fail, but a AR15 back up sight is always there to provide quick target acquisition even when the batteries die at just the wrong moment. Never be caught off guard with our selection of AR15 front and rear sights. If you can't find what you're looking for on this page, use our search bar too look for the AR15 sight elsewhere on our website. Still have questions about which sight is right for you? Our product specialists are waiting by the phone to help you find the perfect fit for your AR-15 Iron Sights or BUIS.