Whistler XTR-695: Why doesn't it pick up cops?

It doesn't warn me of cruisers or motorcycle cops EVER.. why is this? I heard it's because either the Cops use Doppler or they use lasers with a trigger they push when they suspect a speeder. Wouldn't this mean the whole radar/laser-detector industry is OBSOLETE? And people who spend up to $500 on Escort 9500's, Valentine One's, and Bel STI Driver's are WASTING THEIR MONEY?? How can this be?