I carry a Valentine One radar detector in my day bag. I drive multiple cars, so I can I transfer it from one car to the other, and I use it for rental cars as well. A radar detector may seem a wholly unnecessary item for a law-abiding citizen, but as police departments see their budgets threatened, they have become more active in pulling people over for small infractions such as failure to come to a complete stop at a stop sign, or even driving just a few miles in excess of the limit. Modern police radar is designed to be kept in standby mode, activated only when the officer points-and-shoots, but in my experience, many police are lazy and leave their radar guns active all the time.
Since I like to know where they are, the Valentine One is the only detector that shows me the direction of a radar source (whether ahead, behind, or either side). It’s very expensive at $495, but can easily pay for itself, depending on your driving habits. The after-sale service is remarkable; when my detector’s frequency setting drifted after about 8 years, I sent it in and they fixed it and sent it back without charge. They will also upgrade older models for a small fee.