Radar works on different frequencies (bands) like microwaves, invisible to the human eye. For traffic purposes, they are created to go in a single direction, hit an object, and bounce back to gauge speed. It’s effective, but there are some complications. First, radar waves are invisible, so an officer pointing a radar gun at cars several hundred yards away can’t be entirely sure which vehicle being targeted. Radar beams also depend on reflections to get a speed reading, so an unclear path or multiple reflective surfaces can also distort the results.
Now that we have the radar shortcomings out of the way, we can get into the specific frequencies that police use, which you will encounter when shopping for and using a detector.
K-band radio waves are very commonly used in a variety of applications other than traffic monitoring, and thus can be considered the least reliable indicators of police presence. This frequency is often used in vehicles for lane departure warning, blind spot monitoring, speed notification signs, automatic building doors, etc. which can cause a false positive alert.
X-band radio waves are the oldest technology for police radar, and not widely used anymore, which is why often times the alerts from this band are false positives.
Ka-band is the newest technology used in police radar applications, and widely considered the most legitimate notification of an actual police presence. There is a chance for some false alerts from cheaper detector units that leak out this frequency though, but it is less likely.
Laser light is used in some police speed detectors from stationary positions to clock speed, which gives a more accurate targeting of subjects and less room for error. These are effective at about 1/5 of a mile and have a quicker speed read time than radar.