The Caltech campus is very safe according to almost all of the students. Pasadena is one of the safest cities in California; the crime rate is extremely low when compared to LA or San Diego. Caltech security guards are rather friendly (too friendly, according to some) and very helpful. The security guards roam the campus in Daihatsus (little golf-cart-like things) and give people rides across campus if they need them. Students can also call security ahead of time to arrange a ride across campus, which is not really necessary distance-wise considering the school is composed of about a square block; but if students need a ride home late at night, it's there. Security guards are present all over campus every day of the week. Also, extra security guards are seen around the school on days when there are parties or large events just to make sure things run smoothly. There have been instances in which lab equipment has been stolen, but security measures have been increased, and the occurrence of stealing has all but vanished. There is the occasional purse robbery, but it is usually not on campus. Caltech is a very safe place if students follow rules and take proper precautions.
Security in the dorms is much better than in recent years. Ironically, there are no locks protecting half of the dorms, but because the school is so small, intruders would be recognized immediately, so that's not a matter of concern. Most people do not lock their doors, and they really do not need to. Caltech operates on an honor code that forbids stealing, and most students take the code very seriously. Security watches over the students' stunts and antics, and most large-scale pranks are approved by administration before they are carried out. Caltech, as a whole, is a very tight-knit, safe place to be.