I suggest a Trijicon Reflex sight. It is ideal for police use since there are normally no real long shots to take. It has no batteries, is intuitive and quick to use, can take a beating and holds the zero. Precise shots, at the range, out to 200 yds. were so easy they were boring. 300 yds and out, I couldn't make out the target but somebody with good eyes would have no trouble. Also if for some reason you need to use the iron sights, just look through the tube (I used a flip up rear sight and left the front sight in place when I set up my AR).

I have had a long standing interest in the Luepold CQB (I think that is what it is called) sight, the one that can go from zero to 3X magnification. Does anybody know if those work well?