~$275 on Amazon right now), and in my opinion is a worthy investment. I used to be a big speeder back in the day. I've changed my driving habits since then, but I do like to stretch the cars legs from time to time. I mean come on, who wouldn't. Because of this, I wanted an extra pair of "eyes" on the road. Basically, the detector picks up signals given off by police radar and laser guns. I have a lot of hills around where I live, but some folks out west with better conditions have been warned of police radar presence upwards of 2 miles. For me I usually get a half mile warning and I almost always hear the detector before I see the police cruiser. It's an extra layer of defense if you happen to be speeding.
When used with common sense, they can come in handy. Don't go out and buy one and expect to go 80+ everywhere. You'll be screwed in no time at all. However, if you find yourself coasting above the posted speed limit from time to time, this little guy can be a nice reminder to take things down a notch. I have been saved many times and it has definitely paid for itself when you think of tickets and insurance premium hikes. It only takes one or two "saves" for it to be paid off. The most notable example was when I was going about 85 on the highway in my previous vehicle. I had a rabbit (someone ahead of me speeding as well) about 1/4 mile ahead of me. We're cresting a hill and my radar detector goes off. I slow down, he doesn't. The state trooper that was sitting in the median lit him up like a Christmas tree. Now that's not to say I wasn't lucky, because the cop surely could have nailed me too, but I had that little extra warning. The car in front of me didn't.
Since I've had the detector I haven't been pulled over for speeding, and I would say that's an accomplishment with this car. Who knows, maybe I'm just a little more responsible now. If you're looking for a product recommendation, you can't go wrong with the Escort Passport 8500 X50. Buy it.