[hunter2_]

Grocery store motion sensors for automatic doors seem to blast constantly like police sources so those are tough (but primarily X band, which is getting rare for police depending on the area, so ignoring X is an option). But car safety systems are bursty (maybe to reduce power consumption / heat dissipation?), so good detectors are able to filter based on such pulse signatures, basically just delaying the determination to alert by about half a second to see how constant the source is.