We went to the Police Museum last summer because we were doing a unit on crime prevention.  It is a somewhat interesting museum but it is not very big.  It makes up for not being very large by being free.  There are some interesting items you can see including vintage police cars, uniforms, badges and history.  It is a self guided tour which is fine because there is really not much to ask questions about.  The exhibits are labeled and easy to read.

The part I did not like about it was being treated like a criminal to go visit.  It is located at HPD headquarters so you will go through a metal detector, have to show ID and possibly get some attitude to visit.  After that, though, it was a fast but enjoyable visit.  If you are in the area, stop by and take a look.  If you are studying crime, police or something of that sort it may be worth a special visit.  Aside from that, you can probably find more interesting items on the Internet to learn about police. 

The Houston Police Museum is located at 1200 Travis and can be found online at http://www.houstontx.gov/police/museum/.