ACOUSTIC MIRROR: replaces any ground defense object. This mirror has two abilities. 1) no medals may be used to put a flak or searchlight in the same hex as a mirror out of action and; 2) In a target city, the mirror provides advanced warning of incoming bombers and therefore gives Great Britain a -1 VP to the bombing run.
Early Nights comes with three Acoustic Mirror tiles, but no where on the two-sided rule sheet does it say how they are used. Acoustic_Mirror.pdf fixes this. Just print the file and cut the sheet to the size you want.