I bought the SPX 7800BT new for about $150 on 1/18/2015. It’s pretty cool, but you can get a lot of false reports. I’ve read comments on the Cobra Web site that cars with proximity detectors can trigger alerts.
I’ve experienced this myself. Sometimes for no apparent reason I’ll get alternating K and Ka alerts with an occasional safety alert for “Train approaching” (even though I’m nowhere near a railroad).
On the plus side, the iRadar app allows me to have a heads up speedometer using my Android phone. (Of course, I could also use the free Ulysses speedometer for that, but combining the radar detection and speedometer in one application works for me.)