I live in Silver Spring. Montgomery County is going ape with speed cameras. They are even upgrading existing traps from radar to laser plus employing portable laser (and radar) box units chained to telephone poles that they move around like a shell game. They also have installed something I've not seen before (E. Randolph Road between Georgia and New Hampshire Avenues). It's a camera and flash on top of a pole at a traffic light intersection about 15 feet high. I can't get a radar or laser detection from it so I don't know what it is.
I think they are moving to all laser because they know people are more aware of and will likely buy radar detectors than laser detectors and they want to keep making their money.
It's best to at least have a Valentine in your car for laser alerts to these things if you live and drive in Montgomery County. Even though they shoot from behind, you can usually get a signal from the opposite side of the road when approaching a trap.